Expansion tank pressure

One last question, am I correct in doing this.
To get correct pressure in my diaphram expansion tank do I measure the pressure at the faucet with a gauge and then match the air pressure in the expansion tank to that, and check with a tire gauge...is this correct?
thanks
Mike

Measure the water pressure at a hose bib with nothing running in the house, then pre-charge the tank B 4 installing it with the same pressure or less by 2# I like to go 2#s less so the bladder is slightly inflated. Just my way of doing it. The Mfg. says same pressure. Then install the tank.

If the tank is mounted horizontally it needs to be supported.