TF2600 Sensitive Valve Voltmeter
One of the last MI products using thermionic valves, the TF2600 is an AC voltmeter covering the frequency range 10 Hz to 5 MHz and has ranges of 1 mV to 300 V full-scale.
The specified accuracy is +/- 1 % of full-scale at sensible frequencies.
This one is in good working order and is still in regular use.