It pains me to say this, but Art was right.
As a result of the changes I made to the Summary View, I had two fields that were wrong - the Board Width and the Board Length. Fortunately, neither of these would affect the construction of a bowl, but they were wrong nonetheless. I have corrected these errors and as you can see, Segment PRO and Woodturner PRO calculations are now in agreement. The diameters in the two programs were rounded, hence the slight difference. Also, it appears that Woodturner PRO has one more saw kerf than Segment PRO which accounts for the difference in Board Length. I also cross checked them both with other online calculators.
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I have moved this build into production. Here is the link:
http://download.woodturnerpro.com/software/v3/segprosetup.exe