WO1997020188A1

WO1997020188A1 - Level device and method of producing the same

Info

Publication number: WO1997020188A1
Application number: PCT/SE1996/001518
Authority: WO
Inventors: Hans Undin; Åke BACKLUND; Jan-Fredrik Jansson
Original assignee: Hans Undin; Backlund Aake; Jansson Jan Fredrik
Priority date: 1995-11-28
Filing date: 1996-11-27
Publication date: 1997-06-05
Also published as: AU1044797A; SE9504290L; SE9504290D0

Abstract

A liquid level device comprises a longitudinal support member (10) with a least one elongate duct (11) closed from all sides and filled with a coloured liquid (11a) to such degree that in the horizontal position of the duct both the volume of liquid, and the volume of air above the liquid occupy the duct along its entire length. In a preferred embodiment, the support member (10) is made of flexible material so that it also may be wound around a pole-shaped object (12b) such as a lamp post or telegraph pole to determine its vertical position as seen from any direction.

Description

Level device and method of producing the same

The present invention concerns a novel level device with a receptacle which is partially filled with a liquid, and to a pre¬ ferred method of producing it.

As known, level devices are used to indicate the tilt posi¬ tion of an object. Conventional level devices for determining an object's horizontal position comprise a rigid, transparent tube which is curved in the vertical plane and which, with exception of a small air bubble, are filled with a liquid such as coloured water. The tube is mounted in a support member, e.g. a block of wood or metal with a rigid, plane base face, so that the bubble is positioned at the highest point of the arc defined by the cur¬ ved tube when the base face rests on a horizontal surface. The air bubble is then surrounded on both sides by strands of liquid of equal lengt which extend from the bubble to the respective end of the tube.

To determine the horizontal position of an object as seen from all directions, either such a level hasto be applied twice, i.e. in two different directions, or a level has to be used m which the liquid with the air bubble is contained in a circular receptacle with a transparent lid having a concave inner surface. In the horizontal position of the level the bubble is positioned at the highest point of the said inner face, on all sides sur¬ rounded by the liquid.

With the expression "horizontal as seen from all directions" is understood the state of enclosing in all directions an angle of 90° with the plumbline, and in the present description and in the enclosed claims the term "horizontal" is henceforward always understood in this meaning.

For determining the vertical position of a pole-shaped ob¬ ject as seen from all directions is generally used a plummet sus¬ pended on a plumb line. With the expression "vertical as seen from all directions" is understood the state of enclosing in all directions an angle of 0° with the plumbline, and n the present description and in the enclosed claims the term "vertical" is henceforward always understood in this meaning. It is an object of the present invention to provide a level device based on a novel principle and which is less costly in production than a conventional liquid level and which in prefer¬ red embodiments enables the user to readily determine the hori¬ zontal as well as the vertical position in the above stated mea¬ ning.

This object is achieved by the means indicated in the cha¬ racterizing part of the enclosed claim 1, further developments being indicated in the subclaims. With the term "duct" is in the following description and in the annexed claims understood an e- longate receptacle for a liquid which is closed on all sides like a sealed tube.

While the receptacle, i.e. the tube, in the above described conventional level is curved so that its longitudinal axis defi¬ nes an arc in the vertical plane, the entire longitudinal axis of the duct of the present invention is comprised in a single horizontal plane, curved or not in this horizontal plane. This condition also means that the level device of the invention must not be wound around a pole-shaped object along a helical line, but so that the two terminal areas of the duct lie in the same plane. (The term "horizontal" being here used under the assump¬ tion that the respective device is in an untilted position. ) The condition that the base face must closely adhere to the measured object means that the support member must not be loosely wound around a pole-shaped object.

The invention will now be explained more in detail with re¬ ference to the enclosed drawings illustrating exemplary embodi¬ ments, and in which

Fig. 1 is a perspective view of a level device according to the invention,

Fig. 2 illustrates the application of the level device of Fig. 1 for determing the horizontal position of an object,

Fig. 2a shows at a larger scale a cross-section of the level device of Figs. 1 and 2,

Figs. 2b and 2c show in a lateral and in a plan view another embodiment of the level device of the invention for determinig the horizontal position of an object, Fig. 3 illustrates the application of still another embodi¬ ment of the level device of the invention to determine the vertical posi-tion of a pole-shaped object,

Fig. 4 is a perspective view at a larger scale of the device which is only diagrammatically shown in Fig. 3,

Fig. 4a shows at a still larger scale a cross-section of the device of Figs. 3 and 4,

Figs. 5a-c show at a yet larger scale three alternative views of the area V in Fig. 4,

Figs. 6a and 6b show in cross-section two preferred profile shapes of the device of the invention,

Fig. 6c illustrates a preferred embodiment of the foil in the level device of Figs. 6a, 6b,

Figs. 7a and 7b show in a lateral and in a cross-sectional view along the plane VII-VII a terminal plug for the support mem¬ ber,

Fig. 8 illustrates in a perspective view the use of the level device of the invention for determining the horizontal position of a plate-shaped object,

Figs. 9a and 9b illustrate two scales for use with the level device of the invention,

Fig. 10 is a cross-sectional view of another embodiment of the device according to the invention.

Fig. Ila is a cross-sectional view of still another embodi¬ ment, and

Fig. lib is a plan view, on a larger scale, of a vernier scale in the embodiment of Fig. Ila.

According to Figs. 1 and 2a, the device of the invention comprises an elongate support member 10 of transparent material, preferably a plastic material. The support member 10 has in this embodiment the shape of a longitudinal stand or a ruler the cross-section of which has a larger dimension in one direction (left to right in the drawing) than in all other directions, e.g. by having the shape of a trapezium, as is best seen in Fig. 2a.

The lower face of the support member (at the longer basis of the cross-sectional trapezium) defines a base face 10a with which the support member 10 may be positioned in close contact with the object to be measured, and the upper face of the support member 10, at the shorter base of the cross-sectional trapezium and opposite the base face 10a, defines an observation face or window 10b.

A straight, tubular duct 11 is arranged in the interior of the support member 10, extending in parallell with the base face 10a and closed at both ends e.g. by plugs, as will be described below. The duct 11 is, to approximately one half of the volume, filled with a non-foammg liquid Ila with low surface tension and with a different colour than its surroundings, i.e. mainly the support member.

The volume of liquid must not be larger than to meet the condition that in the horizontal position of the device the vo¬ lume of gas, i.e. generally air, that fills the space above the volume of liquid, extends along the entire length of the duct, i.e. from its one end to the other.

The observation face or window 10b, which as seen from the viewer's position, is located above the duct 11, is transparent, which automatically is the case when the entire support member 10 is made of transparent material. The liquid may be e.g. colou¬ red red, which is in the drawing (Fig.5) indicated by hatching. The remaining volume of the duct 11 may also be filled with any other, preferably inert, gas besides air.

A transparent or, preferably, non-transparent contrast foil or strip 10c (Fig. 6a) is mounted in the support member 10 be¬ tween the duct 11 and the base face 10a. Under "contrast" is un¬ derstood another colour than the colour of the liquid, e.g yellow (which in Fig. 5 ofthe drawing 5 is indicated by dots) . The cont¬ rast strip 10c may e.g. consist of a metal foil, preferably 0,075 to 1,0 mm thick, and may preferably be provided with holes 10c' according to Fig. 6c for better fixation to the support member 10. The shape and position of the holes 10c is selected so as to obtain maximum rigidity in the x-y plane.

In one direction, the duct 11 may have larger dimension in cross-section than in all other directions, e.g. as seen in Fig. 4a, and may further have alternating, intercommunicating wider zones 11' and narrower zones 11" for mire accurate reading, as illustrated in Fig. 6. Each zone extends along the entire length of the duct 11.

For determining the horizontal or nearly horizontal posi¬ tion of a surface, such as a plate 12a of a table 12, the support member 10 may be formed in a rigid material, and have e.g. the above mentioned shape of a thick, transparent ruler with trape¬ zoidal cross-section the longer base of which defines a cross- section through the base face. The exact horizontal position of the table plate 12a in the longitudinal direction of the level device is indicated by the liquid volume Ila (Fig. 2a) extending along the entire length of the duct 11 as viewed from above through the observation face 10, i.e. that in the selected colour example the entire duct 11 ap-pears to be red, as shown in Fig. 5c.

When the surface 12a is somewhat inclined, e.g. to the left hand side, only the left hand part of the duct 11 will have the appearance according to Fig. 5c, while the right hand part will be quite free from liquid, i.e. in the selected colour example this part will show only the yellow colour of the contrast strip 10c, as illustrated in Fig. 5b.

The location along the support member 10, more exactly along the duct 11, for the point where one colour is substituted by the other, depends on the size oe angle of inclination, and a scale may be provided on the support member 10 along the duct 11 for reading a numerical value (degrees) of the tilt or inclination.

The zone of the support member 10, more correctly of the ob¬ servation face 10b, which lies immediately above the duct 11 may preferably be shaped so as to show more clearly to the observer the volume or strand of liquid by enlarging it in a direction transverse to the longitudinal direction of the duct. This may be accomplished e.g. by means of semi-cylindrical optical ele¬ ments 10b' according to Fig. 6b, or by prismatic means, e.g. as in thermometer tubes.

Above the duct 11, only a partial zone needs to be transpa¬ rent, so that the rest of the support member 11 or its part lOu (Fig. 4a) between the duct 11 and the base face 10a may be formed in a non-transparent material, preferably in a contrasting colour.

In Fig. 2b is illustrated another method of determining hori-zontal and nearly-horizontal surfaces with an embodiment of the device of the invention. The support member 10 is along at least one of its longitudinal edges provided with a projecting support means 100. The lower face of the support means defines, together with the lower edge or with a part of the lower edge of the sup-port member 10, a second base face of the device, which also ex-tends in parallel with the duct 11 and which allows the device to be placed with the support member 10 on the measured surface 12a in an upright position. A similar support means 100' may provided on the opposite side of the support member 10 to ac¬ complish a wider second base face.

When the level device is positioned on the object to be mea¬ sured m said upright position, the horizontal position of the measured object is indicated by the duct 11 showing along its en¬ tire length the two colours (such as yellow and read) as illust¬ rated in Fig. 5a.

The support means 100, 100' may have the shape of a con¬ tinuous rail, the support member 10 then being unflexible irres¬ pective of what material it is produced from, and irrespective of any rail being provided on its one or both longitudinal si¬ des.

Alternatively, a support means 100 provided only on one lon¬ gitudinal side of the support member 10 may, according to Fig. 2c, be formed with a series of laterally projecting "feet" 100a separated by gaps 100b. This embodiment allows for the use as described above, i.e. analogically to the conventional manner, as well as, when the support member is made of flexible material, in the manners shown in Fig. 3 and Fig. 8.

For determining also the vertical position of pole-shaped objects such as lamp posts, telegraph poles and the like, the support member 10 has to be made of flexible material such as e.g. silicone, so that the level device of the invention may be, as illustrated in Figs. 3 and 4, as a ring R wound around a pole- shaped object 12b. In this embodiment and in this application of the level device of the invention, it is important that the two terminal end portions 10', 10" of the support member 10, and thus also of the duct 11, are positioned on a common level, i.e. that the entire longitudinal axis L (Fig. 5b) of the duct 11 extends in one plane which is a cross-sectional plane of the pole-shaped object around which the device is wound.

The general condition for the arrangement and the applica¬ tion of the level device of the invention is that the longitudi¬ nal axis of the duct must be entirely positioned in one single plane, which in the horizontal or vertical position of the measu¬ red object, is horizontal. In the case of Fig. 2 and Fig. 8 this plane is parallel with the plane defined by the measured surface 12a (nearly coinciding therewith), and in the instance of Figs. 3 and 4 this plane is a cross-sectional plane of the pole 12b.

The support member must not be loosely wound around the pole 12b, but must tightly adhere thereto with its base face. The base face 10a may for this purpose be provided with a longitudinal central recess e.g. as shown in Fig. 2b or at lOf in Fig. 6a.

The vertical position of the measured object 12b in Fig. 3 is indicated by an uninterrupted lower ring of liquid, i.e. a ring in the colour of the liquid, and an uninterrupted upper ring of gas (air), i.e. a ring in the colour of the contrast strip, as illustrated in Fig. 5a, being viewed along the entire circum¬ ference of the pole-shaped object 12b.

In a tilted position of the object 12b, the appearence along one part of the circumfrence will be according to Fig. 5b, and along the other part according to Fig. 5c. Regarding the location of the point where one colour changes into the other, the same applies as was said above about a straight duct.

From a comparison of Figures 2a/5c with Figures 4a/5a fol¬ lows that the exact horizontal position of the liquid/gas inter¬ face in the duct 11 is indicated by the appearance according to Fig. 5c when the level device is applied so that said interface ex-tends at right angles to its base face 10a, and according to Fig. 5a when the level is used so that said interface extends in parallel with the base face.

In Fig. 4 is shown that the two terminal portions 10', 10" of the tightly wound support member 10 bear one against the other, whereby the above said condition, that the longitudinal axis L must extend in one plane, is certainly fulfilled. This condition is also fulfilled when the support member is somewhat shorter or somewhat longer than the circumference of the measured object, and said terminal portions are spaced from one another or overlap one another, as long as it is avoided that the longi¬ tudinal axis L extends along a helical line departing from one single plane.

Also a duct which is shorter than the circumference of the measured pole-shaped object and whose terminal portions are by suitable means affixed to the object at the same level provides the relevant information with an accuracy which is sufficient in many instances, and the accuracy of the determination is of course not at all impaired when the two terminal portions lOx (Fig. 1) of the support member 10 overlap one another.

When the support member 10 is longer than the circumference of the measured object, an alternative embodiment according to Fig. 6 may preferably be used. The support member 10 is there at least at both its terminal portions lOx and at least at one of its longitudinal edges provided with locking means 10d', lOe ar¬ ranged to be interlocked one with another.

The illustrated locking means comprise a longitudinal groove 10d' and a longitudinal crest lOe, both extending along the enti¬ re length of one edge of the support member 10. The groove 10d' is limited by the body of the support member 10 and by a "turned up" ridge lOd, and opens laterally in the direction toward the centre line of the support member 10.

The crest lOe extends parallel and adjacent to the groove 10d' along the same edge of the support member 10, projects in the direction away from the centre line of the support member 10 and has a profile which is identical with the profile of the re¬ cess 10d' . The bottom of the groove 10d' and the top of the crest lOe lie at the same distance from the centre line of the support member 10.

When two terminal portions lOx of the support member 10 over¬ lap one another, the crest lOe of the upper terminal portion lOx may, in the longitudinal direction of the support member 10, be slid into the groove 10d' of the lower terminal portion.

The extent of overlapping which, as already stated does not impair the measuring function, depends on the relation between the length of the circumference of the measured object and the length of the support member.

Several level devices of the invention may also be inter¬ connected to a chain of level devices so as to obtain, if desi¬ red, a greater total length. The interconnection of two neighbou¬ ring devices may preferably be achieved by their terminal por¬ tions overlapping one another and being secured one to the other by means of the described locking elements.

While the device of the invention will preferably be placed on a pole-shaped object at eye level, it is obvious that the ac¬ curacy of the determination is independent of how high or how low the device is affixed to a pole-shaped object. This is an impor¬ tant distinction from determining the vertical position of such objects with the aid of a plummet, because at an equal tilt of the object, a plummet shows a smaller deviation (in terms of dis¬ tance from the object) when applied at a lower level than when applied at a higher level.

It will readily be recognised that the use of the embodiment with a flexible support member is not limited to pole-shaped ob¬ jects with circular cross-sections, and that it may as well be used to determine the horizontal position of plane surfaces. This can be done either in the same manner as shown in Fig. 2 with a device with a rigid support member, or in an advantageous novel manner illustrated in Fig. 8.

According to Fig. 8, a device according to Figs. 2c and 2d with a flexible support member 10 is placed on a table surface 12a or the like in a curved condition, e.g. so as to define a right angle. A horizontal position of the measured object is in¬ dicated in the manner illustrated m Fig. 5a. A conventional wa¬ ter level has to be positioned twice on the surface 12a, e.g. once in the direction of the axis x, and once in the direction

In Figs. 9a and 9b are shown two embodiments of a scale which may be provided on the observation face 10b. According to Fig. 9a, a level device, the duct 11 of which has a length ' and a width B is on its observation face 10b (Fig. 1) provided with a scale S. In said scale S, straight measuring lines M extend ra¬ dially at selected angular intervals, 2° in the illustrated embo¬ diment, from a central point P which is located in the middle of the duct 11, i.e at the half the length 0,5 L' and half the width B.

When the interface between the liquid and the gas, which is e.g. seen in Fig. 5a, coincides with some of the measuring lines, the respective inclination or tilt may be read from the scale. When the interface extends between two measuring lines, the value may be estimated.

Another scale S', illustrated in F g. 9b, and likewise loca¬ ted on the observation face 10b, consists of parallel measuring lines M' indicating e.g. 1°-interval, may be used when the duct 11 is not filled with liquid as far as to half the volume.

The device of the invention may also be provided with seve¬ ral separate ducts located in a parallel side by side relation and/or, as already mentioned, one in extension of the other.

In Fig. 10 is shown an embodiment in which the support mem¬ ber is formed as an elongate, open trough 10' which is closed at both ends, and the walls of which have a height H. The trough 10' is preferably made of coloured (contrast colour) plastic materi¬ al. A separately produced lid or cover 10b" is sealingly affixed to the trough 10' by any suitable means, e.g. by bonding at K and at both ends.

Either the lid 10b" is made of transparent material, and its upper face defining an observation face or window 10b of the de¬ vice and comprising a scale, e.g. according to Figs. 9a, 9b or lib, or the trough 10' is made of transparent material, its bot¬ tom surface 10' defining the observation face, and the other ele¬ ment of the pair, i.e. the cover 10b", being preferably of the contrast colour. A separate contrast strip is then obviously un¬ necessary.

The lid 10b" may be bent at its both ends and possibly pro¬ vided with a sealing compound.Preferably, if the trough 10' and the lid 10b" are made of flexible, i.e. bendable material, so that the device may be used in the manner shown m Figs. 3 or 11, the lid 10b" is located approximately at half the height H of the trough 10', thereby minimizing shear upon bending.

In Figs. Ila and lib is illustrated another way how to faci¬ litate the reading of the numerical value of the measured tilt position. Fig. Ila shows a cross-section along the plane XI-XI in Fig. lib through the duct 11 of the support member 10. The duct 11 has a rectangular cross-section and is positioned edge¬ ways having thus in the vertical direction a greater dimension than in all other directions.

On the inside of at least one of the side walls 11s', 11s" of the duct 11 there are provided at least two, in the illustra¬ ted example three longitudinally and radially extending grooves 120, each one formed e.g. by a pair of parallel, inwardly projec¬ ting parallel crests 120', 120". The radial grooves 120 are angu¬ larly spaced one from the other at selected small angles δ, e.g. 2°.

The system of grooves 120 is preferably located approximate¬ ly at half the height H of the duct 11 for best reading. In an embodiment according to Fig. 10, the grooves 120 may preferably be arranged on the inside of the lid 10b".

When the tilt or inclination is such that the liquid/gas interface Ila' is located in the region of the grooves system, indicating an angular difference of δ ° , said interface Ila' pas¬ ses in a jump G from one level to the next one. This sudden tran¬ sition or "jump" is caused by the surface tension of the liquid Ila. A "vernier" scale such as 130 with values such as 0,1, 0,2, 0,3 ..., indicating frac-tions of the angle δ, may then be con¬ structed according to Fig. lib and located on the observation face 10b for reading the exact position of the interface Ila'.

The device of the invention may preferably be produced, e.g. by known extruding techniques, as "yard goods" from which suitab¬ le lengths may be separated and their ducts sealed at both ends, e.g. by means of end pieces such as plugs 101 according to Fig. 7.

The plugs 101 may have an outer part 101a with the same pe- ripheral shape as the support member 10 including possible loc¬ king means 10d', lOe if desired, and an inner part 101b with the same peripheral shape as the duct 11, or all the ducts in the support member respectively. The plugs are sealingly introduced into the support member 10 and, if necessary, bonded.

The locking means 10d', lOe of Fig. 6 are constructed par¬ ticularly with a view to be used with support members obtained from "yard goods". As they extend continuously along the entire length of the support member 10, they are always present at the terminal portions lOx, irrespective of any particular length which is separated from the "yard goods".

A suitable method to produce the support member for such a device is to extrude it as an endless strip, i.e. the above said yard goods, from a nozzle with a shape corresponding to the cross-sectional shape of the support member, inclusive of possible loc-kmg means 10d' , lOe, a possible foil embodying the contrast strip being also fed through the nozzle.

Claims

C l a ims

1. Level device with at least one receptacle means (11, 111) which is partially filled with a liquid (Ila, Ilia) in order to indicate the tilt position of a measured object (12a, 12b), and with a support member (10) for the receptacle means (11) provided with at least one base face (10a) for positioning the device on the (12a, 12b) to be measured, characterized by the support mem¬ ber (10) having the form of a longitudinal strip and the recep¬ tacle means being embodied by at least one cavity or duct (11) which is closed on all sides and extends m the support member (10) parallel with the base face(s), the longitudinal axis (L) of the duct (11) being in the horizontal position of the device entirely comprised in a horizontal plane, the duct (11) being partially filled with the liquid (Ila) to such degree that in said horizontal position the gas as well as the liquid below the gas occupies in the form of an uninterrupted strip the entire length (L') of the duct (11, 111), reading means being provided to determine from the position of the surface (Ila') of the li¬ quid (Ila) the tilt position of the device.

2. The device of claim 1, wherein said reading means is a transparent observation face or window (10b) through which the duct(s) (11) may be viewed in its/their entire length (L'), the horizontal position of the device being indicated by said volume of liquid (Ila) extending without interruption along the entire length (L') of the duct (11) from its one end to the other, the liquid preferably prefearbly coloured for better discermbility.

3. The device of claim 2, wherein a contrast strip (10c) in different colour than the liquid (Ila), preferably with a plura¬ lity of holes (10c') and made of a metal foil, is interposed be¬ tween the duct (11) and the base face (10a).

4. Device according to one or more of the preceding claims, wherein the cross-section of the support member (10) has in one direction greater dimension than in all other directions, having e.g. the shape of a trapezium wherein the longer basis forms the base face (10a) .

5. Device according to one or more of the preceding claims, wherein the cross-section of the duct (11) in one direction greater dimension than in any other direction.

6. The device of claim 5, wherein the duct (11) has alter¬ nating and intercommunicating wider zones (11') and narrower zo¬ nes (11") which extend along the entire length (L') of the duct (11) .

7. Device according to one or more of the preceding claims, wherein the observation face or window (10b) is provided with op¬ tical elements (10b') enlarging for the viewer the duct (11) transversely to its longitudinal axis (L).

8. Device according to one or more of the preceding claims, wherein the support member (10) along at least one of its longi¬ tudinal edges is provided with a support means (100, 100') pro¬ jecting on at least one side, and forming a base face which al¬ lows the device to be placed edgewise set on the surface (12a) to be measured.

9. Device according to one or more of the preceding claims, wherein the support member (10) with the duct (11) is made of flexible material such as silicone or the like, enabling the support member to be tightly wound around a pole-shaped object (12b) to be measured, the base face of the support member in clo¬ se contact with the surface of said object, the longitudinal axis (L) of the duct (11), including its two end portions (lOx), all positioned in one single plane which coincides with a cross-sec¬ tional plane of the pole-shaped object (12b), said uninterrupted strand of liquid (Ila) which indicates the vertical position of the measured object, having the appearence of an uninterrupted ring.

10. The device of claims 8 and 9 with a support means (100) projecting only on one side of the support member (10), wherein the support means is formed by a plurality of feet (100a) sepa¬ rated by gaps (100b), so that the device may be wound around a pole-shaped object (12b), or in a curved condition be placed on a surface (12a) to be emasured with the feet (100a) pointing out¬ wards.

11. The device of claim 9 or 10, wherein the support member (10) is provided with co-operating locking means (10d'_; lOe) ex- tending along at least one longitudinal edge of the support mem¬ ber (10) at least in the terminal portion (lOx) of the support member (lOx), and allowing for the locking means of the two ter¬ minal portions (lOx) of one support member (10), or for the ter¬ minal portions of two adjacent support members (10), to be inter¬ locked.

12. The device of claim 11, wherein the locking means com¬ prise a longitudinal groove (10d') which peripherically extends along the longitudinal edge of the support member (10) and opens toward the opposite edge, and a parallelly and adjacently the groove (10d') extending longitudinal crest (lOe) having a profile corresponding to the profile of the recess (10d'), so that, in case of with two overlapping terminal portions (lOx) , the crest (lOe) of the upper terminal portion (lOx) may be slid into the groove (10d') of the lower terminal portion (lOx).

13. Device according to one or more of the preceding claims, wherein the support member (10) consists of a selected length which was cut-off from an endless strip produced as cut goods, and of two terminal pieces (101) sealingly attached to both ends of said length, possible interlocking means (10d', lOe) extending along the entire endless strip so as to be functional at any ar¬ bitrary cutting-off point.

14. Device according to one or more of the preceding claims, wherein the observation face (10b) is provided with a scale (S, S') for the reading of the degree of tilt.

15. The device of claim 14, wherein the scale (S) comprises straight measuring lines (M) extending, at selected angular in¬ tervals, from a central point (P) in the geometrical center of the duct (11), i.e. at half the length (0,5 L' ) and half the width (0,5 B) of the duct (11).

16. The device of claim 14, wherein on the inner side of the duct wall which defines the observation face, at least two groo¬ ves (120) subtending a selected angle (δ) are provided, and the scale (130) on the observation face is arranged to enable obser¬ vation of a sudden level transition (G) caused by the surface tension of the liquid (Ila) and thereby vernier-like reading of fractions of said angle (δ).

17. Device according to one or more of the preceding claims, characterized by the support member (10) being formed by an elon¬ gate, open trough (10') which is closed at both its ends, and by a lid or cover (10b") which is sealingly affixed to the trough (10'), e.g. by bonding, and preferably located at approximately half the height (H) of the trough (10').

18. A method of producing a device according to one or more of the preceding claims, characterized by the support member be¬ ing, as an endless strip, extruded through a nozzle from which also a possible contrast foil is fed, the strip being cut to desired lengths, the duct(s) in each cut-off length being to a preselected degree filled with liquid and then at both their ends sealed by insertion of end pieces into the duct(s).