There seem to be continuing online questions about how to select the correct gears for Cirkut cameras, depending on focal length and focal distance.
By inspecting the scales on the bed of my Cirkut #8, I find that there is a simple straight-line logarithmic chart for each distance and all focal lengths.
Note that the x-axis scale is logarithmic and the y-axis is linear. However there is no need to worry about any of that. Choose your lens focal length (in inches) along the x-axis, then the y-axis shows the tooth count of the required gear at 25, 50 or 100 ft. I guess infinity uses the 100 ft setting. A larger PDF version is downloadable from the link below.
It would be a useful exercise to check the data for other Cirkut models, but I don't have those so leave it to others - who may hopefully to publish the results!
An occasional and irregular blog, mostly of photographic experimentation and photographic history.