How can I tell if it works?

[nanafish]

Awhile back I had purchased a Korallin 1502 Calcium reactor off the forum here. Well it arrived in fairly poor condition or the seller just did not fess up about the condition of the plumbing of the fixtures on the lid. I was going to salvage the unit by purchasing replacement parts for it on Marine Depot. It did come with the CO2 gause and solenoid. I am wondering if all this is going to work? How can I tell if the gauge is in working order outside of putting it on a CO2 tank?