How i can record no change by INTERVAL_EVENT element?

Good afternoon, dear colleagues. In data structures information model Data Structures Information Model (6.1.5 Change Data) i see examples how i can record increase\decrease or change of variable, but how I can record no change in variable?
In my opinion i can it only by math_function actual. But maybe there are other ways.
P.S. In ADL i can record 0 in field with increase/decrease math_function, but i dont know is it bug. (see Pic.
photo1696322381
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