Calculations in a query

[dichotomous2013]

I want to perform a calculation that returns a value that is the difference between current month and previous month.

I have a data base for trucks, mileage, hours etc.

So the calculation will be on the Mileage feild. I know how to write and expression to perform a calculation between one field and another, but, is it possible to get calculate the differnce between values using the same feild. I.E

Month January February
Mileage 109000 101000

Many thanks in advance.

[alansidman]

Here is a database that I built for a friend that tracks service and gas usage. Look at the queries to see how this is accomplished.

[ph_jawad]

use "datediff" function in date/time builtin expression builder functions

[dichotomous2013]

Alansidman. Your database is quite cool. I've looked at your queries. It looks like you are performing calculations comparing one field to another. I want a calculation comparing a field against itself. I think the ph_jawad may be onto something with the datediff function, but, how do I build an expression like that in querie? How do I activate the expression builder and what would such an expresison look like?? I am a novice developer.

[alansidman]

Here is a an explanation on DateDiff with examples

http://www.techonthenet.com/access/f...e/datediff.php