spocalc is great, but:
If you have the parts at hand, use your own measurements, not those fro m their list.
I used a wrong nipple seat diameter once, relying on their data. Don't know whether it was a different model year, or the manufacturers data was wrong:
It'd have saved me some hassle just measuring it myself though.
The calculator/the formula itself has worked relyably for me, which i can't say of the calculator on the DT site, which gave funny resu lts for a while some time last year (I've used spocalc ever since).
Tobit Linke, Dortmund, Germany