compute this variance for True North?
The anomaly is truly anomalous: it varies with coordinates relative to the Magnetic Pole, but also with local geodetic anomalies, such as large concentrations of iron; and over time as the M.P. floats around. I doubt there is a formula, although empirical tables must exist.
-- Bill Thayer 41N53 87W38 col cuore a 42N59.5 12E42.4 alt.313m http://www.ukans.edu/history/index/europe/ancient_rome/I/home.html -
