This is a NBS Type 4 (National Bureau of Standards) microwave RF power meter made by TECH USA This RF Power Meter is designed to measure high-frequency microwave power with an external thermistor mount bolometer. This is used in very good condition. It was in working condition when removed from service. The operation and maintenance manual for this is online and can be found with googling (NBS type 4 RF power meter) I do not have the bolometer that was used with this unit.