Mini Lathe DRO Issues

[Toolmaker51]

DRO's count on 2 parameters other than units set for. Those are repeatability and resolution. Repeatability is just as it sounds. Perform a simple test, using a travel indicator; touch off - observe readings - and repeat a few times, both + & - z
Should those be consistent, the likelihood of scale mounting not sufficiently parallel to the axis being measured, is first one suspect.

Resolution is a different issue. Compare a .001 and .0001 vernier micrometer. We can interpolate readings that split .001 observing position of barrel to thimble, but discretion comes into play, is it .2003 or .2004? On a vernier scaled mic we are more sure of fourth digit, leads to estimating the fifth.

DRO's are faced with same, but are interpolating ALL the time, any position other than directly on a particular increment. So, that is 'built into' a scale, an intended resolution. Some readouts have a switch to shut-off display of last increment. Most DRO are 1/2 thou, but they are available in much finer increments,
using highest grade elements that discern (read) increments AND interpolate those in between. (i.e.) A .001 scale doesn't register next increment until crossing the 5th or 6th tenth, it is a quality result of manufacture, potential temperature differential and others less tangible factors. The instructions should cover those.

The other is response speed, few readouts can power up and switch increments equal to feed rate.