Typically daily. They were used for troubleshooting and repairing military avionics. They survived decades onboard ships, etc. They got temperamental in their later years, but we kept them going.
If you have any interest you can search up the (sparse) information on the AN/USM-484 Hybrid Test Set (or System).
If you have any interest you can search up the (sparse) information on the AN/USM-484 Hybrid Test Set (or System).