Do you trust the dial markings or make your own reference points?

On my old Jet pump setup I had a gauge that read about 4 psi high at cut-in and about 7 high at cut-out, which I figured out by borrowing a better gauge from a buddy who does HVAC. Once I knew the offset I just read through it for years. It finally started sticking after a hard freeze and the needle whould jump when I tapped the glass, and that was the point I swapped it. A gauge you have to mentally correct is fine until it gets lazy, then it's lying to you and you don't know by how much.

As for the colored tick marks, I'd assume they were eyeballed. The marks on my old dial were nowhere near lining up with the printed numbers, off by half a graduation or more, probly drawn freehand with the gauge still mounted. If the low-end marks matter for your pump switch settings, verify them with a second gauge before trusting them.

On the little pointer arrows stuck to the glass, I tried one and hated it. It slid around with temperature changes and honestly just added a moving target to an already fuzzy needle. A grease pencil mark on the glass where you want cut-in pressure does the same job for free, though you'll wipe it off the first time you clean the gauge.

For what it's worth, cheap gauges in my basement disagree with each other by a few psi too, and I stopped worrying about it. What matters is watching the same gauge over time so you notice when your pressure tank behavior changes, not which one is perfectly right.

I'm in the replace-it camp on this one. When my gauge started sitting above zero with everythign closed up, that was actually the Bourdon tube getting tired, and mine only got worse from there. Kept 'reading thru it' for a season like folks here are describing and then one day the pressure switch was cycling way off from where I thought it was set, and the pump was short-cycling because the gauge was lying by 10 psi or more at the high end. The offset was not even consistent, it drifted depending on where in the range you were. Here's the thing about those colored tick marks too. If a previous owner marked them with the gauge already out of whack, they're marking that gauge's lies, not the actual pressure. So you'd be learning to read a wrong number against marks made for a diferent wrong number. That math gets old fast. New gauges are cheap enugh that I just keep a spare in the drawer now. When one starts acting wierd I swap it in ten minutes with a couple turns of a wrench, pump off and tank drained down below the gauge first. Then I set the cut-in and cut-out to what the switch is actually supposed to do and mark the glass with a grease pencil if I want a quick reference. No mental arithmetic, no guessing wich scale the old owner eyeballed.

That inner scale is just the same reading in bar, so you can mostly ignore it. One bar is roughly 14 and a half psi, give or take, so the two scales should agree if the gauge is honest. Handy trick actually, if the needle points at 30 psi but the inner number says something way off from 2, the gauge itself is the problem. On the tick marks, I'd check where your pump switch actually cuts in and out with a tap running, then see if the marks land anywhere near that. If they don't, they're probably marking some old tank pressure setting or just decoration at this point.

One thing I learned the hard way with well tanks: the gauge tells you more by what it does between cut-in and cut-out than by any single number. Back before I trusted gauges at all, I'd watch how long the pump ran to fill from bottom to top and time the drop when nothing was drawing. If the needle started sagging while every valve was shut, that meant the tank was waterlogged, not that the gauge was lying. A tired gauge and a tired tank can look alike, so check the tank with a drain-down before you blame the dial. And those eyeballed tick marks on yours, I'd bet money the old owner drew them watching the switch click, not reading the scale.

Update: tried the inner scale trick someone posted and sure enough my needle lands around 20 psi while the bar side reads closer to 1.4, which is a bigger gap than it should be. So now I'm wondering, does a needle that rests above zero always mean the tube's tired, or can these be adjusted back to zero with the little screw on the face? Mine has one and I'm tempted.