A fair number of older adjustable razors just use the blade as the tensioner. The older blades were thicker and as a result had more spring in them so they worked fine. Current blades are a lot thinner and have less spring in them, so the same idea no longer works. If you loosen the head too much it just rotates freely. This was an idea that I came up with to lock the top cap in place which, coupled with the locator pins stops the bottom plate from rotating.

That said, a while later when the Bates arrived, I saw that it used the same system but they added numbers and markings and a stop.
There is nothing really new in the World of shaving - is there!

Its very simple to use, loosen the main part of the handle until you have the gap that you want and then tighten the twist knob and lock the head in place.
Once I got used to it, it is actually pretty easy to adjust on the fly.