This is a great caliper, especially for the low price. It has a little LCD window that displays the reading as well as which mode its readings are in (inch or metric). It changes mode with the push of a button and calibrates the same way. I use mine to determine inside and outside dimensions of materials I use to create models and robotic devices. It takes an R-44 type battery and they send along one already mounted plus a spare. This is my second of these, the first was the victim of a heavy fanny belonging to a friend who didn't look before he sat. Frump, frump, frump.