The reciprocal is your heading ± 180° — the way back. The fast mental method:

• Heading under 180°:  HDG + 200 − 20
• Heading over 180°:  HDG − 200 + 20

(Because 200 − 20 = 180 — it's just easier in your head.)

Golden rule: the last digit never changes. Reciprocal of 167 is 347.

If the first step shoots over 360 or below 0, don't panic — the second step pulls it back into the 001–360 range.