For anyone examining the cruise spreadsheet that was uploaded, I've found two issues to be aware of.  First, for power settings a long way from the setting used in calibration, sometimes the iteration procedure doesn't converge.  For example, if you use data for 75% power at 8000 feet to calibrate, the numbers for 50% power at 14000 feet might not converge.  You need to either fiddle with the start values on the 14000 feet sheet or extend the number of iterations by copying the calculation rows out further to the right in the sheet until they converge.  Second, I checked the spreadsheet to see how well it predicts the numbers from the Columbia manual, calibrating with the Columbia cruise at 81% power at 8000 feet.  Most of the predictions are remarkably similar to the charts (within a knot or two).  However, the farther away from the calibration power and altitude you get, the bigger the error can become.  I suspect the constant propeller efficiency assumption is a major source of the error.  So...caveat emptor...real numbers must come from real flight tests.

Enough math.  Happy flying and building,
Dan