Yup, you need a pressure gauge, attached to an outside tap or appliance valve. No water running - Static Pressure - water running - Dynamic Pressure. I would hope your plumber would have one.
A rough guide would be to turn the hot water on full, get it hot, then turn on the cold, does the hot water drop in delivery?
A rough guide would be to turn the hot water on full, get it hot, then turn on the cold, does the hot water drop in delivery?