Quick tip - Convert 24 hour to 12 hour clock

Lifehacker has this tip

Subtract 10 then 2 to get the 12 hour clock time. For eg.

13:00 --> 13-10 = 3 --> 3-2 = 1pm
14:00 --> 14-10 = 4 --> 4-2 = 2pm
20:00 --> 20-10 = 10 --> 10-2 = 8pm

and so on.