Features The GDM-300/400 Series Hand Held DMM are a compact, high precision, battery operated multimeter series designed to meet most of the daily needs for design engineers as well as service engineers. The GDM-300/400 series design is driven by mobile-oriented features, such as automatic power down to preserve battery life, a large backlight display for crisp viewing, a rotary selector switch and clear-cut push buttons to ease operation. The basic functions match the depth of bench-top multimeters: fuse-protected current input, true RMS for accurate AC measurements, Auto ranging, Duty cycle, and Relative mode. These compact, reliable, and economical devices are ideal for any engineer.