Since you haven't provided any sample events, I'll assume that your event looks like this, in a sourcetype called "X".
2012-09-27 11:09:22 userid=bob A=20 B=30
2012-09-27 11:12:31 userid=eve A=24 B=10
This search:
sourcetype=X | eval AB_diff = A - B | table A, B, AB_diff
would give you the result;
A B AB_diff
20 30 -10
24 10 14
If this is not what you want to achieve, please provide better sample data and more detailed requirements.
Hope this helps,
Kristian
... View more