The positive direction on a clock is clockwise, the way the clock normally runs. You know that if you go clockwise 12 hours, you end where you started. You know that if you go clockwise 10 hours from 12, you end at 10 (2 hours before 12).
Now consider what happens when you move around the clock face in the counterclockwise direction. If you go counterclockwise 12 hours, you end where you started. If you go 10 hours counterclockwise from 12, you end at 2. (You would have to go 2 more hours counterclockwise to get back to 12.)
So, we have described what happens when you move -22 hours (from 12) on a 12-hour clock. The first -12 get you to where you started, and -10 more get you to 2 o'clock.
Now consider what happens when you move around the clock face in the counterclockwise direction. If you go counterclockwise 12 hours, you end where you started. If you go 10 hours counterclockwise from 12, you end at 2. (You would have to go 2 more hours counterclockwise to get back to 12.)
So, we have described what happens when you move -22 hours (from 12) on a 12-hour clock. The first -12 get you to where you started, and -10 more get you to 2 o'clock.
