displaying extruder speed on the fly?

Hi folks,
does anyone know if it is possible to display, say on my glcd, the actual rate
of extrusion at any time? Maybe a simple graph against time.
I'm just wondering if I could watch, say a speedo, as a model prints to see how
fast the extruder is going. It might make working out max print speeds a bit easier.
Not much point slicing a print at 100mm/s when the complexity of means you
can't go fast then 20mm/s


Many thanks