Access 2010: Calculating difference between detail lines

[BobSullivan]

I have a report that groups information by person, then shows a consistent 5 detail lines. Example:

Bob
A 5%
B 2.5%
C 1.5%

Brian
A 6%
B 4.5%
C 2%


I would like to calculate the difference in the percentages between the detail lines so that the report will read:

Bob
Group Percentage Pct-Change
A 5% 2.5%
B 2.5% 1%
C 1.5%

Brian
A 6% 1.5%
B 4.5% 2.5%
C 2%

[HansV]

Is there a field by which the detail records are ordered and that uniquely identifies the detail records?

[BobSullivan]

Yes. The record is listed by rating (the letter) Each of the letters represents a detail line in the report, and each of the names represents a group. The report is pulling data from a totals query that groups information by name and by letter.

[HansV]

Set the Control Source of the Pct-Change text box to

=[Percentage]-DLookUp("Percentage","MyQuery","[FirstName]=" & Chr(34) & [FirstName] & Chr(34) & " AND [Rating]=" & Chr(34) & Chr(Asc([Rating])+1) & Chr(34))

where MyQuery is the name of the query, and FirstName, Rating and Percentage are the names of the relevant fields.