Useful+Excel+spreadsheets

These are some useful Excel spreadsheets.

[|visibility_curve.xls] (note: to process the Bessel function, you need to have the Analysis ToolPak Add-In enabled.) Ever had a problem converting from JD to PTI day-of-year to calendar date (since PTI uses all 3?) This might help, maybe - not really updated for years after 2001. Useful, maybe, for finding known good PTI calibrators.