The M. C. Miller Company manufactures, in-house, two insulation checking instruments under license from the Gas Electronics Company.

One of the instruments (Gas Electronics Model 601) is used to check above ground insulators, while the other instrument (Gas Electronics Model 702) is used to check buried (underground) insulators, via test leads.

These patented instruments have unique designs and they are highly-accurate and ultra-rugged for cathodic protection field work.