Devices and desires

We have had people popping in and out of the engine room this morning with micrometers, with a view to reproducing a nifty little device that apparently only we have:



I don't know what it's called but what it does is to drop the decompressor when you're handstarting it, so that you don't need to take a hand off the starting handle. The spiral thread means that it only happens once the engine has had a good few turns and is hopefully ready to fire. The spring would be attached to a bracket to make it work, but it's taken off for electric starting.