usgs/geomag-baseline-calculator — pull request #137 by emcwhirter-usgs (2014-11-25 22:16:12+00:00)
Title: Gmp 404

This equation may seem confusing since behind the scenes we actually have Ordinate Mean D = **dComputed** = eMean * scaleValue / 60.0, then multiply that by 60.0 since everything is stored in degrees, to get minutes for display.
* Where **eMean** is the average of the 4 'e' values from the real-time data for the entered West_Up, West_Down, East_Up and East_Down times.
* And where **scaleValue** = 3437.7468 / absoluteH.
* Where **absoluteH** = horizontalComponent = correctedF * COS(inclination).
* Where **corrected F** = fMean + pierCorrection.
* Where **fMean** is the average of the 4 'f' values from the real-time data for the entered South_Down, North_Up, South_Up and North_Down times.
* And where **pierCorrection** is defined for a particular pier at a particular observatory in nT.
* And where **inclination** = ((southDown + northUp) - (southUp + northDown) + 360.0) / 4.0.
* Where southDown, northUp, southUp and northDown are entered angels in degrees.

Which would mean that dComputed is actually eMean * 3437.7468 * COS(inclination) / (correctedF)...

But it actually is confusing and should maybe be double/triple-checked at some point. Also, according to Bill Worthington, this is now the correct way to show the equation to the user. (Corrected H * scaleValue / 60)