Just as a thought, temperature change will have an affect on the pressure.The compressed air initially will be hot, when the air cools the pressure will drop sightly.
I once thought about buying such a compressor, but after reading reviews and hearing about people's opinions that such a compressor lasts about 60 operating hours and then requires engine overhaul, I gave up on it.
Yes I was thinking that but the good news is that the cylinders can be removed they are just a hardened sleeve, and the piston seals can also be replaced. They are all avalible from Hyundai