# What is a discharge coefficient and how affects the flow and pressure?

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Marlon Trujillo on 18 Aug 2020
Answered: Juhi Singh on 21 Aug 2020
We can see on Simscape an element called Variable Local Restriction (2P) and one of its parameter is: Flow discharge coefficient
The descriptions says:
Ratio of the actual to the theoretical mass flow rate through the restriction. The discharge coefficient is an empirical parameter used to account for non-ideal effects such as those due to restriction geometry. The default value is 0.64.
But how this can be empirically tuned? How it affects the pressure and flow?

Juhi Singh on 21 Aug 2020
' ' or Flow discharge coefficient is a parameter introduced to account for the difference between ideal(theoretical) mass flow rate and the observed mass flow rate. From the documentation (Variable local restrictions), we can observe that: (Where is the mass flow rate from port 'a')
Therefore, it determines the mass flow rate through port 'a', which in turn affects the pressure.