calculate difference between fields

[alecgreen]

Hi All

I have a table with 3 fields - product group, value & month, each month
I run a append query that adds records to the table. What I am trying
to do is calculated the value diiference between months for each
product group and im stuck!

Thanks

Alec

 

[Jerry Whittle]

Please provide some sample data and the result that you expect.