Jay & Jens, I have used the diagonal method before with one nail in each corner until I got it square. In that case as long as it is not finish work if my cut was off a 16th it did not matter. With using the pocket holes it seems to me the screws will pull it back out of alignment if the cuts are not dead on. John's suggestion of using shims might solve that problem. What do you think? Of course as we all know the real answer is square cuts.
I always use the 3-4-5 for large squares, at 75x40. If you measure 52" on the 75" side, and 39" on the 40 " side. the diagonal will be 65" get it there and screw a 1 by to hold it in place... hope this helps I used this to square 40 feet long with a 100' tape.. math is your friend good luck
Pythagorean Theorem for all right triangles a2 + b2 = c2
In our example a= 3 or 9 b=4 or 16 9 + 16 = 25 square root of 25 is 5 or c=5. For the 3-4-5 triangle will be a 90 degree 60 degree 30 degree right triangle
I'm in no way trying to argue, but a 3-4-5 triangle is not 30-60-90 degrees.
It's more like 36.9-53.1-90 degrees.
You can figure it out with a trig table.
.......................I'm now trying to remember the significnce of the 30 60 90 right triangle.