Difference between 3″ instrument and 5″ instrument

If you are deciding between getting two instruments and your survey angles expected to be within of arc versus of arc for sights of 1500 ft the example below will give you a good idea of what level of accuracy will you achieve with different instruments:

If an angle is expected to be accurate to within (+/-) 1″ for sights of 1500 ft, then the distance must be correct to within
1500(1”)0.000004848 = (+/-) .007272 ft for compatibility.

If an angle is expected to be accurate to within (+/-) 3″ for sights of 1500 ft, then the distance must be correct to within
1500(3”)0.000004848 = (+/-) .021816 ft for compatibility.

If an angle is expected to be accurate to within (+/-) 5″ for sights of 1500 ft, then the distance must be correct to within
1500(5”)0.000004848 = (+/-) .03636 ft for compatibility.