calc chart creation issue

[amplewaffle]

I have a spreadsheet with a date and item column. I receive about 8 different items in varying quantities each day. The spreadsheet tracks which item and how many arrive each day. I want a pie chart that shows me the overall percentage of those 8 items i receive in a month. In other words, for each month, of the total number of items recieved, what percentage of that total is item #1, #2, #3 and so forth. The trouble is every occurrence of each item is treated separately. Instead of a chart with 8 divisions, one for each item, I get a chart with about 180 because item #1 on tuesday and treated as a different entity than item #1on a friday. How do i get the calc chart to label the pie chart field based on the item names, and to calculate the total percentage of each item instead of treating each occurrence separately.