You need to open the screen in Screen4 and modify each DRO that you want to work this way. You will find Screen4 in your Mach3 folder, if not then you should find it on the downloads page. Once you have opened the screen double click on the DRO you want to change and you will see, in the page that pops up, a box for the format string, it will be something like %+.3f, if you change it to %+.2f you will only have two digits after the decimal. Once done save this screen as a different name so that in future upgrades it wont get overwritten. Then when you open Mach go to the View menu then Load Screens and browse to and load the screenset you just saved.
Hood