I am planning on making a hickory backed yew bow.  The stage that I am at now is making the form.  I want to make it back set 1.5" with a 68" length and am wondering if the form needs to be parabolic or round.
A 1.5" back set requires a circle with a radius of 27', and simple enough to lay out with a low stretch string and a pencil.  Read some place how Howard Hill used a simular method to make some forms.  
Now a parabolic arch would be a little harder but I have figured out the function rule for it and could use a grid to make it as well.  
So which is better, or is there no real difference.

Chris;; There is a method using a yade stick: Clamp your yard stick (at a 90degree angle) to your work bench. Now push down on the other end - about 3 in. This will give you a good working arch. Now, transfer this method to your form material.  Clear as mud?  Maybe someone else knows how to explain it better.

thats what i did, bent a batten in a nice fair curve, traced it- chose the best side and transferred it to the other side.
works really well for me!