Foif J2-2 - Page 23

23
3. Index Error
With the instrument in face left, the vertical circle should read 90°00′00″or
270°00′00″when the line of sight is horizontal. If it dose not, the deviation is known
as the index error.
To determine the index error:
Level up instrument. With instrument in face right bring horizontal hair onto a well
defined target. Take R reading, repeat in face left and take L reading, then the index
error is determined as:
For example: L = 86°14′35″ R =273°43′57″
Then i = 44″
Correct value L = 86°15′19″ R = 273°44′41″
For angle measrements with J2-2 theodolite, i of less 15″is usually acceptable.
To adjust:
Open cover (4) the adjustment screw for the vertical index is now seen. The