Extech ex400 series digital multimeter dmm extech ex420 the extech ex420 digital multimeter is a robust and reliable multimeter with an affordable price tag the meter has switchable backlighting to conserve battery life and manual range selection it measures acdc voltage and current plus resistance diode test continuity and temperature it features very low current capability measuring down to 01956a dc for additional safety it has input fuse protection and mis connection warni