I added air to my tires last Saturday using my Kobalt KLDP-1 air pump. I double checked with my Accu-Gage and the pressures were the same. I also checked with my on board pressure reader and again the pressures were the same. I’ve read discouraging posts about inexpensive air pumps with auto shutoff and on board pressure monitoring systems but mine all agree with each other and that’s close enough for me.
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If your entire kit are plus/minus 1psi, then you’re doing better than the vast majority of folks out there. 
My dial-type tire pressure gauge, the indicator on my inflation pump, and the vehicle’s TPMS are all within plus/minus 1 psi of each other.