...okay, don't buy this, or any meter that looks like it! ( pic below) ...the pH is no good at all, probably the worst I've ever seen for checking pH! ...the moister probe is also unreliable, you have to stick your plant in several different spots, destroy'n roots!!!!... you'll get inconsistant readings with this meter all the way around!
...the cheapest thing you can get to check your pH balance is the colored liquid solution that is color coded to identify your ph level...this is very reliable, even more reliable than the electronic meters. Electronic pH meters will give you a more precise reading, however, they need to be recollaborated every so often (attention required) to stay accurate.
...the best method for checking moister levels is to simply learn to
lift your pot... let your plants dry out until they wilt downward...water and count the days before they begin to wilt again...(the trick is to water just before they begin to wilt)... It is a very good idea to let your plant dry ALL THE WAY OUT to make the roots search from moister, as a result, you get a bigger root development and your plant will get to absorb more fertlizers.
...good luck!