How to find magnetic declination of a location?

shouldn't it be minus 7 degrees considering East is Least?

Easterly variation means that the true direction of the magnetic pole is that amount clockwise from true north. Since direction is measured clockwise from the true or magnetic zero the angle will be smaller when measuring a particular direction if the starting point for magnetic is more clockwise than true. E.g. 10°E variation, 33°T is 23°M. "East is least." Magnetic is a smaller number than true.

One should be careful blindly applying the rule. Given the exact same 10°E variation 1°T is 351°M. The magnetic 351 is only smaller than 1 if you consider 351 as -9.

To attempt to answer the original question. Magnetic variation is something you plan for on the ground, either the pilot himself or some squadron planner. The flight plan derived from a map dictates a true course. At several points along this path the variation is accounted for to calculate magnetic course. There is a map with variation values printed as lines with numbers. Then winds are accounted for which gives magnetic heading. Lastly magnetic heading is converted to compass heading (deviation).

So the pilot walks to a plane with a navigational log with times, speeds, distances, compass headings, and blanks to write down the actual times passing each check point for later comparison. Fuel, altitude, rates of climb or descent, times of arrival etc. are also in this log. I have done these sorts of logs in a real airplane to the extent of using different variation values and their averages between points for different legs of the same flight.

The gyro instrument is almost always set exactly equal to the magnetic compass with no adjustment for deviation or variation. It's just a way to have the compass reading more stable to use. What compass heading is needed is either prepared or found quickly with mental arithmetic if not planned for.

There are some interesting files at \DCS\Data\MagVar\COF\ which might be the definitive source for DCS variation data used in game.

I can still remember the T-V-M-D-C sequence used in basic flight planning from years ago.

• You draw the departure to destination line on a map and measure its direction. It is TRUE, so that is the 'T".
  
• Apply the Variation 'V" to get the MAGNETIC direction 'M'.
  
• Do your sums to allow for forecast winds and apply the drift correction to get the magnetic heading you wish to fly.
  
• Take this number into the cockpit and find the little correction card near the compass and apply the correction ( the DEVIATION 'D') to the 'M' and get 'C' which is the COMPASS heading to fly.
  

Then go flying and find that the winds are not as forecast so all your sums are wrong anyway. :doh: