Can anyone help with the following?

I have a spreadsheet with yearly hours budget/actual for my dept. of 24000 hours, which is divided into 26 fortnights giving 923hrs/fortnight. In 1 row I have the budget filled in for the year(26 cells of 923 hours). In the row below this, I have the

*actual*worked hours, which are updated fortnightly.

Is there a formula which would show a running difference between fixed budgeted hours and accrued hours, shown in 1 cell, which gets automatically updated as the previous fortnight's actuals are updated, so I can quickly see how w are tracking?

Any help appreciated.

/Gelaw