via Bulletin 17b "Guidelines for Determining Flood Flow Frequency"
The NRCS Frequency Curve Determination spreadsheet has several advantages over other free programs developed by U.S. government. For example, the NRCS spreadsheet gives the user complete control over the graphics and also provides a button for precisely reading values from the curve.
This Microsoft Excel spreadsheet was developed by the NRCS Water Quality and Quantity Technology Development Team, has been tested, and correctly reproduces the results of examples in Bulletin 17B "Guidelines for Determining Flood Flow Frequency", revised edition, March 1982. The spreadsheet employs macros which are safe in this version at the time downloaded. The user is cautioned that proper use of the spreadsheet requires training in hydrology and statistics.