All metal. For determination of wavelength and velocity of sound in air by resonance of air column. A mounted is sturdy, plastic frame with transparent front and back windows. One side of frame has color-coded, 4mm socket terminals for electrical 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. Tuning fork required for experiments (not supplied).