Pivot Chart Average of Differences

Hello all,

I am trying to create a pivot chart for the following data Attachment 543691

I am trying to get a pivot chart to display the Tool Num as the categories (easy). The difficulty I am having is displaying the number of parts made per tool because for every Tool Num, the Number of Parts Made displays at what total part quantity was the tool replaced and I need to find the average of the difference for each tool

For example:
Tool Num: POT 6
The tool is changed at 30 part and 60 parts
so the average would be 30

when this excel sheet is used data will be continually entered in chronological order but there may be instances where Tool Num names are not the same between sheets so sorting and calculation before charting hand doesn't seem to be an option.

Any help will be very much appreciated