Subtracting from previous record in a report

[todmac]

Hello,
I have a report (based on a query) that lists the date, and number of Kilometers at each data entry.
I want to show how many KM's there are between entries, so I need the most recent entry - the second most recent entry. Then the second most recent entry - the third most recent entry and so on.
I have played around for a whle now and looked everywhere online, but I am not clear on the easiest way to do this. Help?
Todmac

[June7]

Not really sure what you want, but for one possibility, review http://allenbrowne.com/subquery-01.html#AnotherRecord

Or maybe you want a running sum. Textbox in report has a RunningSum property.