Download Anida Technologies dual digital and dial caliper simulator app.
Designed for tablets but works on phones as well.
Use the app to measure inside or outside features in either 0.001 of an inch or 0.01 millimeters as a real engineering tool (actual resolution will depend upon your device screen).
As a teaching tool, you can read the dial face and then switch to the digital face to confirm your measurement.
Anida Technologies is a contract engineering company in Dallas that provides electro-mechanical design and training services and can be contacted at www.anidatech.com.