Digest Number 2937 - Steps per inch

In following the discussion on calculation vs. trial and error setting of
the spi I would like to relate my experience and ask if it makes sense or is
way out of line.

I initially set the spi by calculation; sherline supplied standard lead
screws 20 tpi X 200 steps per motor revolution X 4x stepping equals 16000
steps per inch, Correct?

However when I measured the travel (at several places along the axis) using
MDI commands my dial indicator repeatedly indicated that 16070 steps were
necessary to get 1 inch of travel. Similar experience (slightly different
numbers) on the other axis. Does this sound reasonable or do I have
something to track down? And what might it be?

PJH