Not sure exactly what you are after, but "trust" the reading you are seeing. Just know that it could be a little bit to either side of the reading. 0 might not be true 0. 0.04 might be 0, that's why you need to couple observation with testing. If you are getting algae on the front glass every couple days and you are showing 0, its probably not true 0. If you have pale corals and go a week without cleaning the glass, and you have a 0.04, it might actually be closer to 0.
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