Here’s another piece of “legacy” technology. However, in this case the manufacturer, Spellman High Voltage Electronics Corp in New York, still offers this device as the HVD100. This is the smallest model, for up to 100K volts. That’s 100,000 volts. The input voltage can be monitored at a ratio of 1,000 to one, or 100V full scale, or at 10,000 to one, for 10V full scale. The total resistance of the column is 1,000 Meg ohms or 1 Gig ohm.
I bought this unit on eBay as basically a piece of junk. I was curious what it was, as the description wasn’t clear. It arrived slightly damaged. I disassembled it and altered it a bit to strengthen it and make it easier to take the top and bottom electrodes off. All the rounded parts are for the purpose of reducing arcing. Arcing will interfere with measurements, creating momentary lower-resistance paths across the device. However, the top and bottom electrodes make it really clumsy and difficult to transport. It is designed for laboratory use, and includes a sparse but descriptive label and BNC connectors to attach measuring equipment.
As with many of the items I have kept around, this one has a certain aesthetic value, but I never use it. Though I find high voltages exciting, they are difficult to produce and dangerous to handle, and really beyond by current experimental capabilities.