What the hell is this?

Inspected a 1966 12th Floor condo yesterday. And saw this inside a closet. The condo is heated by Baseboard Water Heaters and Common Water Heater (?).

An ideas?

Hydroponic boilers have a cut in and cut out control. This gauge might be the pressure at which these baseboard heaters are on or off.

I’m not very experienced at boilers but that would be my guess.

Pressure regulator control likely controlling a valve as Paul said

Well it definitely is a pressure switch, but where is the furnance on the 12th floor? What was it connected to?

Paul, I had assumed the same as well, but have never seen one before, let alone above the shelf in a closet that was tucked away in a corner. I almost missed it. My first OLD condo with boilers, so I wasn’t sure what I was looking at.

Marcel; I have no clue. Walked up and down the hall and did not see any doors other than each individual units entrances. And, of course, nobody on site that could answer either.