Error Prevention:
Having observed various types of possible errors during compass surveying, the surveyor has to take adequate measures during actual use of instrument to minimize the effects of these errors. Some of these are provided below.
Ensure Horizontality of Needle and Scale
If the needle is not horizontal even when the compass is levelled properly, a small coil of brass rider is used by sliding it on needle towards the higher end of needle. Proper adjustment of rider will make a needle and scale horizontal.
Ensure that Pivot is Central to Scale
Readings at both, North and South, end of needle are recorded. The difference shall be exactly 180o. Any deviation from this will indicate that either the needle is not straight or the pivot is bent. If the difference between N- and S-readings is constant for different positions of compass, though it may not be 180o, it will indicate that needle is not straight while pivot is in centre. The needle is carefully straightened and observed to erase this deviation. If the deviation is not similar for variant compass position, pivot bending is indicated. Pivot is bent and needle straightened to remove this error.