Wow:
>>so a 3.8 x 3.8 mt roof has to basically be square with an error only 2 mm...
My maths is a bit rusty, but isn't that around 0.05%?
Asking a lot, but good luck with it.
My feeling is that things like gate openers are built to be big and bulky and forgiving of things like dust and grit build up in the grooves- not so observatories!
As you chase down the last irregularities hopefully it will all slide together for you.
Neville
LSO