I purchased a quick-read temp probe - different reading than the pit probe

I have a 4.2 heatermeter. I use a thermocouple for the pit probe.
Recently, for homebrewing, I bought a handheld quick-read temp probe - cheap China off of ebay. I thought I'd compare the readings in my Costco Pit Boss grill.
With the probes within 1" of each other, there is a 30F difference. The thermocouple reads 30 degrees lower than the handheld temp gadget.
I'm guessing I should not put in a -30 for offset for the pit probe.....but question what to do.
The China hand-held reads near the same as the grill temp sensor at the top of the lid.
Suggestions?

Do an ice water and boiling water test and see how they both read.

Yeah there should be 0 or 1 degree offset in every setup, because if something is off by more than that then something is wrong. A simple one-point calibration will make that one point accurate but usually shift everywhere else off. Boiling water is a good test though, and you can also check at the thermocouple output where it should be 0.500V at the boiling point at sea level. Check it using the big empty circles by the amp itself. The one on the right edge is ground and the one to the bottom left of the amp is the output.