Beginner on event studio - problem with condition of a task

[Sunchaser]

Dear all,

/* Environment:
. IBM Cognos 10.2.2
. Oracle 11g
. Windows Server 2012 R2
. "Full Control" -> I mean we are admin, etc, etc
*/

Sorry, I'm lost ... I try to set-up a task that would generate a report when a value in a table > 0. I would need this task to be perform one time, and only when the value changes from 0 to 1.
. I have defined the event condition ("[TASK_STARTED] > 0", where "TASK_STARTED" is the name of the field)
. Then I have defined the task: run a report and save it on the file-system
. Then, I tried to set-up task execution rules, may be the problem is here ...
I kept only the "New events" ticked in the "For selected events:". Well ... I'm not sure it is the correct way, but nothing else is working.
. Then, I have scheduled the agent, nothing particular here; I choose for testing "every one minute".

What happens is the following: when the schedule is enabled, and as soon as the value has changed from 0 to 1, the report is generated every minute, even if the value is changed back to 0 !
(at least, positive point, the report is generated successfully)
Well ... I feel I'm doing something wrong, correct ?  :)

Can somebody tell me how I can achieve my small test ?

Thanks !
Kind regards
Vinc.