/diy/ - Do It Yourself

Weston clamp-on multimeter Model 633. It is about 14 inches long and weighs a couple of pounds. It does not work. I have been unable to find a manual. It seems they were available starting at least in the early 1940s and up until at least the mid-1960s. This was their 'low range' model. It starts at 10 amps and goes to 1,000. It could also measure up to 600 volts.

I tested it by clamping it around a few different power cords around the house (PC, running microwave, 40-watt lamp) and the needle does not move no matter what the setting. What should I check first? It does not appear to use a battery. More pictures to follow.