Originally Posted by
60av8tor
Free up the gray matter for more important stuff. Reciprocal course for the hold... use +2/-2. Either add or subtract 2 to the first digit and do the opposite - add or subtract 2 to the second digit:
236 inbound: subtract 2, add 2. 056 outbound
058 inbound: add 2, subtract 2. 238 outbound
Obviously reciprocals of headings <180 are fairly easy in your head. You’re merely adding 180. But this trick makes >180 - where you have to subtract 180 - much easier.
I found it easier to memorize the reciprocals than do math with ATC yelling in one ear and the engine fire bell in the other.
You only need to memorize increments of ten, the ones digit is obviously always the same for the recip.