... is to invent a Mitre gauge.

No electrickery allowed.

Basically it is used to halve the angle in a join so that the 2 pieces of wood can be sawn and then joined to make that angle.

I am sure it is very simple but too early in the morning to get my brain round it.

BTW no cheating, this has been invented.

Easiest way is to draw it on a piece of paper then fold it in half

Oh no. A compound mitre? I rued the day this subject ever got brought up again. Took me days to understand how to do them on the front of my car. Basically, if it helps, how I finally got it was by starting from the max measurement from the other end and then measuring down by the required angle (a) on one face and then down again by the next angle (b) on the next face and then go up on the next face by the angle - a and up again on the final face by - b. Or summat like that

the way I would do it wold be to have one gear inside a larger inner gear that has twice the number of theath wit an idle gear in between; one gear connecto to one arm and the other to another arm.

so when one arm is moved, the other arm moves half the distance hence gives half the angle.

guess I am gonna have to google it to see if that is correct or how itr is done.

I have a feelking it can be done using a mirror too but not figure that out as yet.