The human finger, is the most accurate water meter ever invented. Dig your finger in, feel if there is moisture. Feels dry = you needed to water yesterday. Feels lightly moist, just barely damp = perfect time to water again, feels wet = do nothing, check again tomorrow.
Also lift up the pot every time you check with your finger. Notice the "heft", a light pot is dry, a heavy pot is wet. Soon you won't have to poke your finger in, as the weight of the pot will tell you everything you need to know, once you calibrate your sense of weight.
Some will stick a bamboo skewer into the media. Leave it 24/7 stuck in the pot. Pull the skewer out, and notice the color change. The dark area is wet. When the skewer gets "light" below the soil line it is time to water. I personally use my finger, instead of the skewer, because the skewer method has led me to run too dry. But that is me, some swear by the skewer method. Depends on how adverse one is to sticking a finger in the dirt.
Electronic moisture meters are notoriously faulty at giving a accurate moisture reading. The human finger is far more accurate than any $100 meter. True industrial meters, that run into the thousands are quite accurate, but bonsai should be a tactile hobby, don't trust a cheap electronic gadget.