Hi Mat,
Would agree with Mike about plugging in a pressure guage.....I have the same.
I use this, but gradually wind up the pressure so as not to dammage the guage.
Find a pressure that you are comfotable working with. I find 250 to 300 on a porty is fine with a 2 jet wand, 500 psi may well empty your tank fairly fast without improving results.
John