I am sure someone else has suggested this but here goes:
Lathe Work 101:
Turning a shaft down to size:
Old Way:
Measure the stock, take a cleaning cut (to round the stock) then measure again.
On a piece of paper: Subtract desired from actual and divide by 2 (depends on your dials!). This is then the amount to remove.
Take more cuts and repeat the above until finished!
New Way:
As most of us use digital callipers:
Round the work as above.
Manually set the callipers to finished size and then zero them.
Apply callipers to work, measure, and divide the reading by 2 – no need for paper!
Ok so this is for getting very close, a precision mike is still the way to go