Internal signals and local auxiliary variables are "Local data" in Stateflow®:
All local data of a Stateflow block must be defined on the chart level or below the Object Hierarchy.
No local variables may exist on the machine level (that is, no interaction should occur between local data in different charts).
Parameters and constants are allowed at the machine level.
By Task > Modeling Standards for MAAB > Stateflow > Check Stateflow data objects with local scope