Del, working on English longbows I can take about 15 seconds before I start and run some numbers and know exactly what the bow will look like when I am done. Based on weight and what job the bow will be doing I can use the math to select the best wood for the job. Even though the math is more of a rule of thumb and not an exact science I guarantee it will get you close enough for an excellent start. Some experience does come into play with knowing what to do with the numbers.

Yeah, I s'pose I'm being disingenuous as I do something similar...

But if you can do it in 5mins it's arithmetic not maths

I s'pose I have a bit of a bee in my bonnet about maths, I'm ok to a point but dropped out of uni' 'cos I couldn't handle the higher maths, I was frustrated that I had better understanding of the physics than most but couldn't cut the maths... Sums me up, I'm an empirical guy.

I still have have a calculus book on the shelf that sits there accusingly.

Del