I used to rate them negative because I used the tremolo wrong. I didn't know that to change the color you have to insert the end of the strip with four colored rectangles. I figured any piece of paper would work because I've seen that happen in the past. However, I find them extremely difficult to use. The color change is hardly noticeable. I love the tester you dip it in and it changes color based on PH. I don't know, they seem strange to me.
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