Time card calculation formula explanation

Hi,
I am now responsible for calculating time from employees time cards. We had a time clock that was using hh:mm where the mm was a number between 0-99. That time clock broke and I bought a new one and set it to calculate hh:mm where mm was 0-59.

About this same time is when I was told to do the time cards. The spreadsheet was setup to use the mm as 0-99. Consequently timecards were miscalculated for about 2.5 months. Average overpaid was 2 hrs each 2wk pay period per employee. (

So, I found a calculator that uses this calculation for the hh:mm that is for 0-59.

=IF(AND(B4<>0,C4<>0),IF(C4<B4,C4+1-B4,C4-B4),"")

I would like to understand this formula. I have used excel a lot and have a basic understanding of formulas. <> is not equal to, "" is empty cell?, I think! Anyways, this formula works for entering time but I want to understand how it works.

B4 = time IN
C4 = time OUT

Thank you for your help!

Mick

wat u are going to do

Oh, thank you so much!!!