I've had an old fashioned one where you have to work it out for a few years now which is not as easy to use as a micrometer but a bit more versatile with having a larger range and doing both inner & outer diameters. Then last year I saw some really cheap digital ones on Ebay and thought "why not, it's cheap enough to leave in the workshop all the time ?".
Yep, pressing "zero" and then simply reading off the numbers is definitely the way to go !
Brian