It can be mounted permanently measuring through hole in fire door. I don't have mine measuring constantly but I check the draft often. Baro will mostly be used to adjust draft but air shutters on combustion and stoker blowers can be tweaked also. Keeping the draft where Keystoker recommends will ensure efficient coal usage.
Normally people run metal brake line tubing or small copper tubing from the hole in the door several feet and then connect the plastic tubing that comes with and attatches to the manometer. The manometer is mounted near the boiler or a stand can be made or purchased which will allow setting the manometer on top of the jacket.