I have one of those, and I just don't use it, I think mostly because the scale seems arbitrary to me, and at least the one I have needs to be set fairly deep to get a reading, so it is not as if I could tell how much moisture there is at different depths. So I look at the grass for signs of drought stress and, if in doubt, try to stick a screwdriver into the soil. If I get a lot of resistance, it is time to water.

Just my $.02 of course.