The more complex ones can have 100 or more sets of zeros so you can set a zero for each of the holes in a part or a set of parts and zeros for the corners of rectangular holes, the 1/2 button for setting part centre is very useful.

You can also get a box that scales plug into which connects by USB to a PC running a program giving you a "PC DRO".

Mine are all SINO type from Machine DRO, some have been running 24/7 for over 10 years, I'm sure you can get the same stuff cheaper but I go back to Machine DRO because they do support the products they sell.

- Nick