I have conducted pressure drop testing for a blast damper, the data has given readings of pressure drop and velocity.
I need to produce a pressure drop and face velocity graph to represent the data and this is where I need a bit of help.

How do I calculate face velocity? And can someone kindly explain to me what face velocity is and why this information is important??

I have googled info on face velocity but I'm going round in circles and genuinely need some help.