
I am a professional HVAC technician and have several high-end professional sensors. I got this for a friend who I teach work to. This will work for a beginner. The problem is that the bottom arrow is offset by 3 dots, it should be at 0 not 3. So when I try to calibrate it back to 0 the pan head screw is locked on the screen I try my best. to turn it and it's just blocked.

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