It was purely mechanical. Somehow I managed to find the model: https://www.ebay.com/i/203083047312 https://www.ebay.com/i/203083047312 A closeup picture of th

It was purely mechanical. Somehow I managed to find the model: https://www.ebay.com/i/203083047312 https://www.ebay.com/i/203083047312 A closeup picture of the dial: https://i.ebayimg.com/images/g/aogAAOSwFmZfPquw/s-l1600.jpg https://i.ebayimg.com/images/g/aogAAOSwFmZfPquw/s-l1600.jpg The log-factor wasn't as severe as I had remembered, but the 0-1m angle is about the same as the 20-25m angle. It was still pretty easy to get 15s, 30s, etc. I'm sure you could do a lot better with modern digital electronics.