“In the early 1980s Robert MacPherson needed a way to measure the thickness of the raised helmets he was making. His prototype “deep caliper” used parts from a machinist’s indicator set and a 3/8” rod. This simple device could reach almost anywhere on a piece of armor, but it was finicky to use. The frame was not stiff enough and the effect of gravity could cause the reading to be off by several thousandths of an inch.

By the early 2000s, Mac had plans for a stiffer caliper with a welded sheet metal frame, but his friend Sean Powel thought it would be a better tool if the frame were an aluminum casting. They experimented with plywood mock-ups until an essential geometry emerged. Sean used his training as a mechanical engineer and ability with CAD to have a model printed up in plastic.

The project languished a bit till Patrick Thaden offered to cast up a frame for the prototype. The result worked well. It was convenient to use, could reach almost anywhere, and was stiff enough that gravity did not affect its accuracy.

Early 1980’s model 2000’s model comparison