Q: What time is it when your clock strikes 13?
A: Time to get a new clock!

Explanation: When a clock “strikes the hour” it means that it is exactly on the hour, 8:00 or 11:00 for example (not 8:17 or 11:36) and the bells will chime.  Here is Big Ben striking the hour.

On a clock or a watch, the only numbers you see are the numbers 1-12; there is no 13.  So if the clock strikes 13, there is a big problem!  Yes, at 13 o’clock you will need a new clock.

(Some readers might argue that the military and some countries use the hours from 13 to 24 to talk about the hours after noon.  Point taken.  You will, however, not see the number 13 on the face of a clock, only on some digital clocks.)

Here is a brief history of how we keep time: