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In my experience only running +30 would indicate magnetism.
This is a good point. I have started testing all of my new watches for magnetism. My latest rep (ZF BB58) showed up highly magnetized. I bought a cheap demagnetizer off aliexpress and it worked great: LINK
Here is a great article on how to test for magnetism and demagnetize a watch: How to Demagnetize a Watch
Quote from the above article: There are apps that utilize the magnetic sensor on a smart phone to detect magnetism. Example of these is LEPSI on iOS, or Physics Toolbox Magnetometer on android, or in general apps that have the name “magnetometer” or “gauss meter” will do.
I have used the Physics Toolbox Magnetometer app on my Samsung phone and can confirm that it works great.