A) Never rely on gauges at filling stations & buy two really good professional gauges, preferably different brands (even the best aren't exactly expensive). B) Check one gauge against the other regularly to ensure accuracy. C) When you've checked the pressures then reset the reference values. D) Check the tyre pressures often as ambient temperature has a large effect. E) Only check & make alterations when tyres are cold, which is another reason not to check at a filling station. F) Buy a decent tyre inflator to re-inflate tyres at home (because they should never be warm). G) Unfortunately I've not found one TPMS that's 100% accurate but the ones on my 718 are far better than many, including the system on my wife's BMW 2 series & her previous 1 Series.---------------Other than that there isn't much to say other than if you do the above & you keep getting trouble then get the system checked by your Porsche centre.