For experiments on properties of wave motion. Moving coil type, 30 X 15 X 30cm, with spring control and magnetic damping. Basic movement of meter calibrated to 5mA, 100mV. Long, pointer, needle, with thick arrowhead for clear visibility from a distance, moves on hardened and polished steel pivots and jeweled bearings. Mounted is sturdy, plastic frame with transparent front and back windows. One side of frame has color-coded, 4mm socket terminals for electrical connection, and a slot for inserting or removing scales; other side has zero adjustment knob for locking pointer needle. Any one removable, large scale with graduations on both sides can be selected from demonstrates meter.