PH AND MOISTURE METER BY GARDMAN

I've been a bit concerned about whether or not my Prunus avium Stella Gisela 5 will be getting enough water or not.  It's a tricky thing when plants grow outdoors in tubs that can be a bit temperamental, trying to decide whether they need watering or not.  I can well believe it when I read that the majority of plant nurturers kill off their plants with too much water in a panic not to give them too little.  Roots need to breath oxygen too, just like us.  I generally can tell if a pot needs watering by the weight of it (or pushing my finger into the growing medium) but there is no way I can lift that heavy terracotta pot now it is filled with planting compost and a small tree and the situation has been further complicated by my covering the surface of the pot with a deep layer of bark as a mulch.  So, I have bought a PH and Moisture Meter by Gardman.   Of course, it is going to come in useful for other plants too regarding moisture content and PH level.  I already know that my soil leans towards acid but all the same.   I was really surprised to discover that the meter reacts immediately upon inserting the prongs into the soil - no waiting for the gauge to decide whether or not it will go up or down.  How clever!  I assume there is a battery or two inside.