Page 425 equipment and instruments 4823 



the sheet so that the ends of the scale coincide with the minutes of longitude and so 

 adjusted that the scale crosses the latitude line at the correct position for pricking the 

 longitude directly on this line. 



4823. Lockerbie Diagonal Scale 



The Lockerbie scale is designed for scaling geographic positions m meters from 

 survey sheets or for checking the plotting of stations. It is made by photographic 

 methods in the Washmgton Office and is provided for a scale of 1:10,000 only. The 

 graduations on the underside of a rectangular piece of thin glass are protected by a 

 thin layer of transparent lacquer. Tests indicate that distances may be measured 

 with this scale with an accuracy of three-quarters of a meter at a scale of 1:10,000. 



The scale is divided vertically into 20 equal spaces of 100 meters each by numbered 

 horizontal lines parallel to the bottom edge of the glass. The initial horizontal line is 

 actually omitted, but 0.2 mm above and below its place two horizontal Imes are ruled 

 in order that the projection line may be centered between them. The horizontal lines 

 are crossed by 20 vertical lines equally spaced at an arbitrary distance representing 

 a 5-unit interval. Every alternate vertical line is numbered beginning with zei\o at the 

 left. Each long rectangle formed by adjacent horizontal lines and the outside vertical 

 lines of the scale is accurately divided by a fine diagonal line from the lower left corner 

 to the upper right corner. The diagonal Ime must be very fine so that it may be placed 

 on and exactly bisect the station dot, when used in scaling. This arrangement of lines 

 serves to subdivide the 100-meter intervals so that, in scaling, distances can be read 

 directly to the nearest 5 meters and may be estimated to the nearest half-meter. 



Method of use. — The lower edge of the scale is placed against a straightedge near 

 the position to be scaled. Both are moved around on the sheet until the parallel below 

 the position is exactly between the two horizontal lines at the initial of the vertical 

 scale. Holding the straightedge firmly in this position, the scale is slid along it until 

 a diagonal line bisects the position dot. The number of horizontal lines above the 

 projection line gives the dm. or latitude distance (see 7411) to the nearest hundred 

 meters, to which are added the 5-meter intervals, as indicated by the number of 

 vertical lines to the left of the position, the meters and half-meters being estimated 

 from the adjacent vertical lines. In like manner the scale is centered over the meridian 

 and the dp. or longitude distance scaled. 



The Lockerbie scale is most advantageously used on sheets m which there is no 

 distortion; otherwise the scaled values must be corrected for the distortion (see 7361). 



4824. R.A.R. Velocity Scale 



The R.A.R. velocity scale (i^in fig. 91) is used to convert time of sound travel in 

 sea water into horizontal distances at the scale of the survey, thus greatly facilitating 

 the plotting of R.A.R. positions. The scale is approximately the same length and width 

 as the meter bar. It is divided from right to left into 50 spaces, each representing the 

 distance traveled by the sound wave in 1 second of time. A subdivided space at the 

 right permits settings to tenths of seconds directly, and to hundredths of seconds by 

 estimation. 



From bottom to top the scale is divided by equally spaced horizontal lines, one for 

 each velocity of sound from 1,460 meters per second to 1,540 meters per second at 5-meter 

 intervals. Each of these lines is, in effect, a separate scale. When using a velocity of 



