Calculate occurrence/thousand from table

Hi all,

Problem:

I have a table of data (see attached), that starts in the first column with a date. Each row then contains an 'occurrence' against that date; the number of rows showing the same date depends on how man occurrences were recorded for that day. The last column has a volume number which contains the total volume of an object for any particular day. So, on any particular day we have several occurrences recorded against a known volume for that day.

What I need to do is: 1000/volume*occurrences (the volume and occurrences are date specific). So for any given date i will be able to calculate in one fomula the volume and occurrences to give me the occurrences/thousand figure, make sense? I suppose the sum of any particular date is te same as the sum of occurrences as each occurrece is recorded on a seperate row as the row will contain specific information not included in the attached. But for this calculation, i only need to know the sum of occurrences for each day and calculate the occurrence/thousand figure aainst the days volume.

Thanks