Thanks for all the help, Muirenn. I'm probably being a bit of a pain here. Are you Irish by the way? Muireann (with an 'a' usually) is an old Irish girl's name?

That last link was really useful. That girl is amazing. How she kept going with all those injuries is unbelievable. Fair play to her. Great info too.

Basically, my problem is that I can't guess how much air to pump into my tire when it's already inflated because my gauge doesn't say how much pressure it's at already. So if I was able to attach my floor pump and see that it was at 100 PSI already, then I'd know that I just had to add 10 PSI more from my pump (as an example) to make the pressure inside my tire become 110 PSI. At the moment, I can only attach the pump and add more pressure until the tire goes hard (so I start at 0 PSI on the pump gauge and go up to 60 PSI as an example). But this doesn't allow me to know what the total PSI in the tire is at that point because the pump gauge would read 60 PSI at this point, when the pressure inside the tire could be 110 PSI because I started with pressure already in my tire (or I'm guessing even 120 PSI if the pump isn't allowing me add more air and the tire feels completely rigid, since 120 PSI is what the manufacturer gives as the maximum tire pressure). I hope that makes sense.