In message , Grimly
Curmudgeon writes
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Richard saying
something like:

I had wondered about making accurate 90 deg corner plates at home and
taking those to site to use almost jig-like to ensure accuracy. Might
that work?

Of course.

Just check the diagonals are equal

regards

--
Tim Lamb