Transmit/Receive Discards Alert Trigger

I have an alert setup that sends an email when transmits and/or receive discards have reached at least 100 for the hour.

The problem i am having is that the email keeps getting sent over and over again, with the same number of discards for the hour.

I only want the alert to trigger when the number of discards has changed; how do i go about changing the trigger?

Thanks for your time!

V/R