I am handling a vintage 1998 Cassens & Plath Horizon sextant in effectively new almost untouched condition.
I notice that the swing arm spring tension is very light. It engages reliably without any wobble...and stays in place. I see no play with light finger pressure but I was somewhat surprised at its soft engagement, as the aluminum astra has a much thicker single leaf spring as opposed to the two spring stack, and has a much more tight engagement.
There seems no way to overstress the C & P as the handles come together..so it seems intentional, and it lightly stays engaged. THe brass is finer cut than the aluminum, and from my dumb mechanical engineer perspective light engagement on those delicate teeth makes a lot of sense wear wise (the lower the face pressure..lower the wear) , especially as I notice on the astra its easy to drag the worm if careless.
I have no guidence on what rack tension should be other than no play. I wondered in the past if the Astra's face pressure contributes to rack wear on the aluminum sextant body.
I also wondered if it is related to the rougher finish material needing more force for precise engagement.
Does this spring pressure observation sync up with anyone elses sextants?