GB257059A - Improvements relating to levelling staves and like surveying instruments - Google Patents

Abstract

257,059. Sterr, W. C. van der, and Watts & Son, Ltd., E. R. July 6, 1925. Levelling-staves.-The face of a levelling or like staff is divided into a number of equal areas by means of sloping graduationlines, and each area is subdivided into a number of equal areas by lines parallel to the longitudinal axis of the staff, the areas being distinctively marked so that a reading can be taken without the use of any figures or numerals. Fig. 1 is a broken elevation of a ten foot staff graduated for reading in decimals of a foot, and Fig. 3 shows part of the staff as seen through an inverting telescope. Each foot is divided into ten equal parts such as a<0> - - a<9> by sloping lines, each part being also bisected by a sloping line. The face of the staff is divided by longitudinal lines into five strips each <1>/20 ft. wide so that each main division (<1>/10 ft.) is divided into ten lozenge- or diamond-shaped areas. The gradient of the sloping dividing lines is 1 in 5, so that the lowest point of any given line is in horizontal alignment with the highest point of the next line above. The main divisions are distinguished by bracket marks such as the arrow indications l. Alternate areas both laterally and longitudinally are made black and white for convenience of viewing. The markings which obviate the use of figures are as follows :-Supposing the ten areas in each main division to be numbered 0 to 9, as seen in Fig. 3, then in a given foot all the divisions have a distinctive marking such as red colouring, indicated by vertical hatching, in the same numbered area. For example in the divisions b<0> - - b<9> the red colour is in area number 1, in the divisions c<1> - - c<9> in area number 2 and so on. The first decimal place is indicated by circles m, n. marked in appropriate areas. Thus in the divisions a<0> - - k<0> the circle is in area number 0, in the divisions a<1> - - k<1> it is in area number 1 and so on. The second and third decimal places can be obtained by observing the position of the horizontal crosswire p in relation to the divisions on the staff. With the cross-wire in the position shown in Fig. 3 it is seen that the red area is in position 6 and the circle m in position 8. The second decimal place is obtained by observing which area has its upper edge intersected by the crossi wire. In Fig. 3 this area is in position 6, i.e. the red square. The reading thus far is therefore 6.86 feet. The third decimal place is obtained by estimating the distance from the top left-hand corner of the area concerned (number 6) to the point of intersection, in relation to the width of the area. If this distance is nine-tenths of the width the reading to three places of decimals is 6.869 feet.