1. Tyres will expand and contract, and after some driving the
tyre is hot and expanded. Maybe you pumped it at 210 while it was
hot, then it cooled down a little, contracting and making the
pressure higher?
Whereafter you inserted the nozzle again, the tyre released the air
trying to match 210. But maybe when you plugged it out, some air
got out so it went below.
Then finally you plugged in again, so it went up to try to get
210.
You can't get the exact pressure and maintain it la.. roughly can
already. When you insert and remove the nozzle, sure got some air
escape, so the reading won't be exactly what you pumped
previously.
2. Once in a fortnight should be ok. But if u happy, check more
often also good. Also always check for nails and stuff embedded
when you wash car or when you are pumping air.
Tyre loses air through the tyre walls itself.
Some tyre shops offer nitrogen pumping into the tyre for about
$10-12 bucks. It leaks slower than normal air.
