We have this discussion every few months.
First - tire gauges are not accurate. Actually we don't even need an accurate tire gauge. Since all gauges are inaccurate we want to be sure they have the same inaccuracy every time we use them.
This is called repeatability.
The secret here is to use the same tire gauge every time you check your tires. Using different gauges is where people get in trouble.
Tools for your tires.
Richard Newton