4 ms·
Don't some maps actually show the current rate of change? I seem to remember some of the USGS maps I purchased showed this.
by mordechai9000 5y ago
Don't some maps actually show the current rate of change? I seem to remember some of the USGS maps I purchased showed this.
- deleted 5y ago[deleted]
- ls65536 5y agoYou're right that they do often show the local magnetic declination's rate of change (around the time of publishing), but even that goes out of date eventually. For relatively short periods (maybe on the order of years or possibly even a decade or two, depending on the particular location), applying this rate of change may give a good approximation of the present day's magnetic declination value, but beyond that the errors can become unacceptably large.