Have you ever gotten a mild shock from an electrical appliance in you house. It could have been caused by poor isolation or current "leakage".
This project is a Meter for measuring high resistances (up to about 3 000 000 ohms or 3M). Most cases of poor isolation you will encounter will involve high resistances.
To test for leakage in an appliance you must first unplug it. DO NOT TEST AN APPLIANCE THAT IS CONNECTED TO ANY POWER SOURCE.
Then connect one of the Probes to the plug of the appliance and touch the other Probe to the metal parts of the appliance. If you get a high reading, you may have poor isolation and a shock hazard. This circuit can be used to measure any large value resistance.