date opbject??

Hi,

When i place an date in the C colum the number in the B colum is added by 1.
What i realy want is that the number start over again with 1 when i put in the next month.

Like 1 to 20 inputs for the month januari en when februari comes Nr. starts over again with 1.

Here is an screenshot of the situation:

http://www.wens.speedxs.nl/excel.gif
I am dutch so "ALS" means "IF" in the formula: =ALS(C4="";"";ALS(B3="Nr.";1;B3+1))

Thanks in advance.