Tire pressures

I put an aftermarket TPMS on my old Tacoma. It read the individual tire pressures, but indicated lower pressures than my 3 or 4 pressure gauges, which pretty much agreed with each other. I replaced the '09 with a new Tacoma, which reads tire pressures. The readings are low compared with my gauges, on the order of the aftermarket TPMS on the old truck. What am I to believe?

 

Believe that one or more tire pressure(s) are lower than the others when the TPMS warning is indicated.
Other than that, I find the PSI reading useless.
Use an external gauge to check “true” pressure.
That’s my opinion anyways?

 

Sensors are imperfect devices calibrated by imperfect humans with imperfect devices. Cheaper ones are expected to be imprecise. Certain TPMS sensors you must think of as devices that output information proportional to pressure but do not output pressure values accurately.