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: