The transits are intended for use in surveying operations. Class A covers an instrument of minimum weight, small dimensions, and compactness for use where those factors are of essential importance consistent with the required accuracy. Class B covers an instrument of medium weight and dimensions for use where transportation is not a critical problem or where circles larger than class A are desirable. Class C covers an instrument of maximum weight and dimensions for use where transportation facilities are readily available or where a higher order of refinement in determination of angular values is required.