Something I was taught when I was an apprentice at sea; with Noah, just in case anyone asks
:
CADET
Compass (bearing) to
True (bearing)
ADd
East
Therefore if the Magnetic variation is 11.3°E
C AD E T
180° 11.3°E 191.3°
or
C AD E T
168.7° 11.3°E 180°
so if you want to point your mount due south, your magnetic compass should read 168.7°
Hope this helps and I haven't added to the confusion