Drive Speed?

I Have A Wrapper Where Conveyor Speed Slows Down For No Apparent Reason.the Machine Has An S7 300 Plc And I Have Pinpointed The Problem To A Mul I Block The En Is Speed Entered At Hmi And The In2 Is Set At 19 But Changes To 18 For No Apparent Reason Thus Causing Speed To Decrease.can Anyone Help?thanks

What variable is used at In2 (e.g. MWx or DB1.DBWy)

the variable is DB11.DBW16.thanks

Right Click on the variable (whilst not monitoring) and then select GoToLocation to see where the variable is modified.