magic probe hacklinger gauge

Hello!I am building instruments for hobby ....i want to make a hacklinger gauge for measuring top thickness of guitars....this already exist you can see it here Magic Probe Electronic Thickness Gauge - YouTube i was told that it can be built with adruino and a hall sensor and then with simple programming.....the problem is i dont know how to do it...does someone in here have an idea?thanks alot in advance for your help!