Extech 412440-S Calibration Source Checker Easy to use pocket checker for simulating current Loops Pocket Checkers are easy to use and provide a quick and easy way for checking calibration of meters or controllers Instantly determine if your device needs calibration or if sensor needs to be replaced 0.1mA accuracy Current: 4mA, 12mA and 20mA; overload indication when load exceeds 240Ohm