anybody use?

[sierra22]

In the name of "KISS", I can suggest doing as the Swedish army and use both Ridgerunner and Boyds approaches.

Set up a BDC calibrated for standard atmosphere (SAC).
Use a Silva weathermeter or similar and measure pressure/temperature/ wind, look in the datatables and add/substract pre-calculated values based on the measured deviation from SAC.

Works vey well, even when you're getting tired and stupid. Put up a "fill-in-the-blanks" chart and you can doublecheck your calculations should you miss. But you are looking at $80 for your ring and $150 for the weatherstation!