Yes, it is a Tachymeter scale, plain and simple. But it is marked for slower speeds than the customary Tachymeter scale, that has higher speeds on the right side of the dial (and particularly the top right quarter).

In the photo below, if someone took one minute and nice seconds (69 seconds) to cover a measured mile (or kilometer), then the speed would be 52 miles (or kilometers) per hour. While this may not seem very useful, I would point out that in my own travels, I am more likely to be moving at 52 miles per hour (over a measured mile) than 380 miles per hour, which is the speed shown on the "normal" Tachymeter scale, at the nine second mark.

So that's why this unusual scale was used for the Solunagraph . . . much more sensible for measured miles on the water (lake, river or ocean) than the usual scale (which might be useful on a racetrack).

Jeff

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: Oddly enough, the left side is part of a tach scale, but the ride
: side is not. It's like half tach, half countdown. It's puzzling
: alright. Beautiful watch though....