Oh ok. That makes sense now. Cheers.

Do you think it would be best for me to always pump the tyre up to max (assuming that this means it's at 120 PSI which is the manufacturer's maximum tyre pressure) and then let some air out and then pump up to what the correct tyre pressure should be (using the formula you linked to)? Otherwise, I could buy a separate type pressure gauge which would measure the pressure and then use my pump to get to the PSI I need.