Note:Because most of the cost is put it on the pump, so the barometer is just for reference, it's not accurate. but the pump surely can create a pressure up to 120 psi, you can feel it,also can use an accurate barometer to test it. hope understanding

When you blowing up a tyre:first  choose the correct valve(A/B) Second pull down 1 to status 2 then lock-in.And you could blowing up the tyre now

Without Pressure Gauge