How to accumulate time

is there another way to measure the time intervals between cells and accumulate them into a single cell? I've included a sample of the worksheet for clearer reference, please refer to sheet 2.

it's a wireless punch card system, naturally the odd cells (column A,C,E,G,etc) denote 'IN' while the even cells denote 'OUT'. the time difference is basically

(B1-A1)+(D1-C1)+(F1-E1)+... *to count time in the office
(C1-B1)+(E1-D1)+(G1-F1)+... *to count time OUT FROM the office

as you can see from cell B6, my formula is trash and probably is erroneous too. (ignore the "time out from office" column). Also the actual number of IN-OUTs could very well reach 10x or more, so a code with loops or something would be more viable, right?

can someone help me through this?

thanks a lot in advance!

~Michael

anybody? please?

after reading another thread, i think i got it, by just using

=B1-A1+D1-C1+F1-E1+H1-G1

and formatting the cell as (time) [hh:mm]. didnt know i could do that, so thanks to vbanoob for answering.