Before using the caliper, be sure to zero the jaws. Just close them fully and press ZERO. You can set a zero point at any location of a measurement by pressing ZERO. 

• Be sure there is no debris blocking the jaws from closing completely when setting zero.
• The little knob along the top edge of the caliper will lock the jaws. 
• You can read the scale printed on the caliper body if you like.

The jaws are hardened steel and can be used to scribe marks on various materials if desired.

I use this for depth measurements, diameter measurements of screws, drill bits, and many other smaller width precision measurements that are under 6 inches.