Right angle layout with a trammel
While a square corner can achieved with 3-4-5 or the square root of 2, I find doing it with a trammel easier.
First layout a baseline.
Set the trammel at whatever radius suits the job, A-B, swing a short arc across baseline both ways from A to B
Now set the trammel about 1/3 longer than the A-B radius.
Swing the short arc B-C from both ends.
Now, draw a line from A to C
Presto, square corner, guarantied.
I probably did a poor job of explaining this and is elementary for some,but maybe some can use it.
I'll try to show a square inscribed in a circle tomorrow.
Royce