The Tektronix Type Q is a strain gauge preamp plug-in for 500-series scopes. The Type Q contains a 25kHz oscillator that is used to drive a Wheatstone bridge for measuring the impedance of the strain gauge. Resistive, capacitive, and inductive strain gauges are supported.
Type Q was introduced in 1960 and was the last all-tube plugin. It was dropped after 1971 or 1972.