Beersy said..
Forget about the gauge, It's unnescessary...
Actually it is, if the kite has a two way pump valve. I prefer them as they allow the gauge to give a reading and you have more precise pressure applied to the kite, at least to meet manufacturer's recommended pressure (usually around 5 to 7psi). Of course the other way is to simply bend the wing tips after pumping the kite and see if they bend easily. If they do, you need to pump her up more!