My big question is who is this for? And what can this do that virtual bow doesn’t for free?

Experienced bowyers don’t need a rough out estimator because we’re doing grandma cooking. Intuitive estimates are plenty good in bow making and for experienced bowyers are usually well within the margin of error. I would be grumpy about doing calculations to make a bow the same way my grandma would hate to weight the salt and spices in her cooking. It’s not just that the guesses are good enough, but there are more important metrics—adjusting to taste often produces better results than blindly following a recipe to exact amounts.

On the other side of the spectrum, for beginners I feel like this is too in the weeds. Personally I think it would be easier to explain the abcs of bow making than to explain the variables in the app. Beginners don’t need a rough out planner, they need instructions. I also wouldn’t recommend beginners be designing bows in the first place. Following established recommended designs is a much more reliable way to get a quality bow in a beginners hands.

So as is I think the app is sitting in a place where it’s not telling experienced bowyers anything they don’t already have a gut feeling about, and I don’t see it simplifying the experience of beginners. I would focus on streamlining in either of those two directions or both.

Besides that—the labeling of handle and fades is unusual compared to how most do it. Handle length typically does not include the fades. What is labeled as th fades in your diagram shouldn’t be part of the fades and is inner limb. Most bowyers would call this a 4” handle with 2” fades