Mox - the basic technique is to paste your photograph into a graphics program like Windows Paint or MacDraw or some such. Then you use the Oval tool (every program has one) to draw a horizontal oval on top of the picture, with the top center of the oval on the center of the bow. That lets you easily see where one limb, or part of a limb is not following the curve in the same way that the other is...
I have a Macintosh computer, so I use the AppleWorks Draw program that come with it. Here, for example is the final tiller-tree shot of my "Second-First" bow.:
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