I don't know if it's been posted before, but an excellent piece of work has been done by Stu Miller with his dynamic spine calculator. It can be downloaded here , don't forget to download the instructions, also.
I think it's a godsend. It pretty much eliminates buying several shafts and doing a lot of fiddling. I have a 36# recurve and bought some GT Ultralight 600s. I plugged all the parameters into the program for the arrow and my bow. The program said a dynamic spine of 44.3# was required by the bow. I put in different values for both the arrow length and point weight to come up with that same value for the arrow. Voilà, perfect flight. Note: for the GT UL 600, under "Arrow Shaft Size" I had to choose "Other" and put in the three required parameters.