My application calculates accumulated flow. One of the rungs accumulates the flow of Flow2, and it works properly. The identical code for Flow1 is not working; it accumulates then decreases the accumulated flow. Flow1 is always a positive number, so it should not be subtracting the accumulated flow. It looks like there is a synchronization problem for storing and retrieving the accumulated flow value Flow1_Accum.

The problem was the accumulated value was in %MD15.  The register needs to have an address that is a multiple of 4 (20, 24, 28, 32, etc).  I changed the address to %MD96 and that fixed it.