Automatic Magnetic Declination in ike

The digital compass in ike uses magnetoresistive sensors to measure the heading to magnetic north, but to calculate the correct position of a remote target, the heading to true north is required. To calculate true north, the magnetic declination must be known. To make matters worse, magnetic declination varies not only with your location on the earth, but also drifts over time. However, all of these difficulties are easily overcome using ike's automatic magnetic declination feature.

The National Geophysical Data Center (NGDC) provides a mathematical model of the magnetic field worldwide, that can be used to calculate the magnetic declination for a specific location at a specific time http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml.

ike uses this mathematical model, along with the current time and your GPS position to update the magnetic declination each time a new GPS reading is received, so you're always up to date.

I recall once many years ago I had to demonstrate an ike unit in Taiwan before we had automatic magnetic declination implemented. I had forgotten to check the magnetic declination before I left home, and didn't have Internet access. I had to find two find two landmarks about 100m apart, measure their GPS positions using ike, work out the true bearing between the landmarks using ArcPad, take bearings between the landmarks using the compass in ike, and finally calculate the difference between the true bearing as indicated in ArcPad, and my measured value to compute the magnetic declination... It did the trick, but boy what a hassle!

These days I just leave the "Automatic Magnetic Declination" option enabled...