if i buy a prv how exactly do you work out how to set it?
i think you do it from your boost gauge but how do you know if its accurate and your setting it correctly?

Fit it, take it for a spin, read the boost gauge, adjust it a bit if necessary, trial and error until you get the boost you want

well at the moment my gauge is reading about 17ish psi on the gauge but dont know how accurate it is.

Probably accurate enough, but if it's a piece of cheap sh** then you could invest in a better quality gauge for peace of mind...

only just got it a month ago.
i spoke to someone when i got it and they said 17ish is about right.
am i right in thinking that standard a boost gauge should read lower in 1st and 2nd cos of the limit thing?
and with a chip it would be about the same?