Tire Gauge to Avoid Over-Inflation
The pressure dial doesn't measure the pressure in the tube - it gives the pressure in the entire system (tube + hose).  When you connect your pump, you need to pressurize the hose to the same level as the tube before it will read anything.  I usually find this takes two or three full pumps, and the resistance jumps up massively once the tube and tire have the same pressure. At that point, the dial will show you the pressure in your tire.