I am installing 3 meters to monitor solar panel output. I can use a clamp meter to check the amperage and during the tests it will read 1 to 6 amps. The meters read 0 to 2 amps. I have tried to calibrate them and I can get them to read correctly but as soon as I take the screwdriver away they return to the lower reading. How can I get them to accurately. I have tried reversing the shunt wires and get the same result. Is there a better meter that will work, I am ready to return these.