crafts help: why do you measure a wood frame diagonaly - Help.com

Howdy — I am pretty sure that measuring diagonally is the only way to ensure that the frame will be a perfect square or rectangle. If you don’t measure the diagonal relative to the two perpendicular sides of the frame, then you could end up with a parallelogram instead of a square or rectangular frame. How the the length of the diagonal factors into this is as follows:

take length of the horizontal side of the frame x itself (meaning, horizontal length squared)
plus
length of vertical side x itself (same calcuation as above)
and then divide by
length of the diagonal

The result of this calcuation should be 1.

That’s how you can ensure you’ve got a perfect rectangle or square. It’s based on the Pythagorean theorem. There is a good tutorial here if you wanted to learn more about how it works:

http://www.arcytech.org/java/pythagoras/.

Hope this helped. By the way, please be sure to fill in your ‘About Me’ post — it sounds like you are into DIY, crafts, gardening, and wood work, and we could certainly use your help answering other people’s questions on the site!