Bicycle hand pump pressure gauge
I have a Topeak "Road Morph" mini pump on my bike, and the pressure gauge on that is at best a distraction. The display is a bit of plastic sliding in a tube, so there's a lot of friction and that makes the pressure reading unreliable. It can stick anywhere, but usually it reads low, like yours does. That makes it useless for anything other than "is there air in my tyre", which I can answer more easily by squeezing the tyre.




So it's likely that the reason you're having problems is that your pump is a cheap version of mine, and it works even less well than mine

The effective pressure gauges that I've seen are all dial gauges, and there are not many mini pumps that have those. Normally they're found on floor pumps like this: