GUILD/FACTOR.Ok we have all heard of it !but for me it can get confusing , I get the principle,but can someone clear it up once and for all,it's obvious your boards volume is in there ,then your body weight and do the math !=G/F ...My point ,for clarification ,board volume+ weight of board ,fins ,leash ,deck pad ect ,rider weight ,wetsuit, boardies ect,absolute total mass above water = load ? Therefore more accurate G/F ?.

Do not try to get a GF as accurate as possible, as it is an approximation anyways.
Shape is more important than getting the GF as "realistic" as possible.

For instance for my 97kg, I am as stable on a 105L wide-at-the-tips board than a 120L pulled-in tips shape.

Just be consistent and use the same as everybody else:
board volume as given by the manufacturer (so naked, without pad nor fins)
rider weight as given by your bathroom scale.

Adding board + paddle + (wet) wetsuit weight gives a more accurate figure (and useful: 1.0 is then archimedes float limit) however, but do not call it "Guild Factor" to avoid confusion.

Thanks Colas ,I'll stick to keep it simple

I've got two boards very similar volume and size but one is quite a bit more tippy than the other. It's all in the shape, rails and volume distribution. Over time I just know what approx volume I'm comfy with and for my waves.