This question is of importance because there are now a number of alignment systems on the market, using different methods. To answer, ask yourself the question: What do I want to accomplish? You want to bring offset and angularity within tolerance.
Rim & Face measures the offset through the RIM reading and measures the angularity through a face reading which can easily be inaccurate if the diameter at which it is measured is small such as 8″ or less, or even wrong if the shaft floats in or out during the measurement.
Reverse Indicator takes two rim readings which establish the offset and compute angularity from the difference in these offsets. It is not affected by moderate shaft float but is only accurate if the distance between the measuring devices exceeds 8″. Also, accuracy is dependent on measuring resolution which in case of laser systems should be at least 5 microns if you expect to see improvements over normal dial indicator readings.
Offset & Direct Angle: Since offset and angularity is what you were out to measure, obviously a system measuring the RIM and DIRECT ANGLE is best, particularly if it also has a measuring resolution of 1 micron (.00004″) like our SHAFTALIGN, OPTALIGN SMART, ROTALIGN ULTRA laser alignment tools.
by Ana Maria Delgado, CRL