difference between values accoring to dates

[anna anna]

if i have a table with dates and nr ie:

1-11-10 - 300
2-11-10 - 400
3-11-10 - 500

how is the smartest way to find out the difference of 2 numbers by entering the according 2 dates

ie from: 2-11-10 (400)
to : 3-11-10 (500), it sould come out 100.

i can enter the previous date (with calculatedate -1) but i can not enter the according date of it, and then calculate the difference.
thanks in advance

[NeoPa]

Not much info to work with here Anna, but basically you would subtract one from the other. If I try to provide anything more helpful I keep coming up against the lack of usable detail to work with.

I'm sure we can be more help, but you'd need to explain the question better first.