bike wrench

Hello everyone.

I recently got myself a mountain bike from Canyon. It all works, got myself all the gear, pumps and all. And the pressure gage give me a reading of 10 PSI, which is odd because the tires are firm. 10 PSI should be nearly flat.

I have other pumps, including one that works for my car too, which I trust because I cross checked its values with my mechanic.

Here's the odd thing. I got the bike out and plugged it to the car tire pressure device and it also gave me a reading of 10 PSI. I also have a Topeak Shuttle Gage, 10 PSI.

How is that possible? I can't really believe all three readings come from faulty devices so I'm thinking I'm the one doing something especially stupid, or maybe a defect somewhere on the valve/tire but it's brand new, so I think I'm the one to blame. Any ideas where I've been an idiot?

I did open the nut on the presta valve prior to taking measurements.