585.—To Determine Horizontal Distance in Chains the stadium should be marked as just described for feet, but at 20 links distance from line to line. Then the radius 150,000 × 20 gives 3,000,000. Taking for example, readings as before with difference of 3285 we have—
3,000,000 3285 = 913·2, or 9 chains 13·2 links distance.
To Determine Horizontal Distance in Metres, the stadium is divided to 4 metres. Then radius 150,000 × 4 = 600,000. Taking, for example, difference of reading as before 3285 then
600,000 3285 = 182·64 metres.
586.—Levelling—Taking Altitudes.—To take the elevation of the staff above the level of the instrument, subtract the reading of the scale, when the axis of the telescope is level, from the lower reading of the staff on the scale, and divide by the distance difference, as found by the method discussed before, then multiply this by 10 feet. Thus taking the lower reading as before 64,450 and the constant for the level position of the instrument, say 50,010, we then have—
| Lower | reading | 64,450 |
| Level | " | 50,010 |
| Difference | 14,440 |
then
14,440 3285 × 10 = 43·96 feet nearly.
The heights, in relation to the position of the instrument, are positive or negative according as the scale readings are greater or less than the constant level reading or departure point.