Let me set out my lathe dials before we start
1. its metric
2. the dials are graduated to take a curt off the dia. eh dial up 1 and the dis. will reduce by 1mm
so to take your digital calliper / digital mic and zero it and sett it to the dimension you require
then set the indicator to zero at this setting
then measure the part in the lathe
the resultant measurement is the amount to take off , you can then plan your cuts before hand , so no more cut and try
another tip with a digital calliper when you need to measure the centers off two identical shafts ( or holes if you put in test pins ) zero the calliper
measure one of the shafts/pins
zero the calliper at this position
measure over the outside of the shaft/pin that is the centre to center measurement
hope it helps
Stuart