I'm learning the use of PHI in art. The various roots, baroque diagonal, etc. It's a bit complex, but I'm eager to begin using these in my work.

One thing I have not seen answered anywhere is how to apply PHI (whichever root you use, 1.333, 1.618, etc) to a non-standard size surface. That is, a painting surface that doesn't accurately correspond to one of those roots. Take for example a surface I have now, which measures 53 x 40". This more closely works with 1.333 (1.325 is what mine reduces to). But then, I could always just draw an accurate root 1.618 space onto this surface, using the leftover margin as "dead space".

Surely the old masters ran into this from time to time.

I've also thought about getting a PC/Mac projector and simply projecting the desired root onto my surfaces and tracing from there, to save me the monotonous task of measuring, etc.

I'd appreciate any feedback. I could be over thinking this as well, since I'm still learning the theories. But, I am a perfectionist and I like accuracy

Thank you.