Compass heading

True → magnetic → compass. Variation is signed East-positive ("east is least": magnetic = true − variation); deviation is the signed correction from your aircraft's compass card, added to magnetic as the ASA CX-3 manual's worked example applies it (203 T with 4° W variation and 4 deviation → 207 M, 211 C). Check the card placarded in YOUR airplane — deviation is aircraft- and heading-specific.