It's 3:20. You want to know what time it'll be after 2:50, but it's hard to do it in your head, since the minutes sum to more than an hour.
So, you do this: you convert 3:20 to 320, and 2:50 to 250. You sum 320 and 250, and then you add the time constant of 40, to obtain 610. That converts to 6:10, the desired time.
Why did God make time like this? Why is the time constant forty?