how to give negative alert thresholds?

Hi,

I need to have the alert range say,

Minimum to -25%

-25% to -15%

-15% to 0%

0% to 15%

......to Maximum

The target is to acheive 0% (like in the variance scenario)

The problem is I can represent the negative values in the alert thresholds!

Is there any work around?

Any help appreciated!!