This meter is only designed for testing voltage. Two threading ports on the two sides, one side is for battery/mod,who has 510 threading, the other one is for 510 atomizers. When battery is turned on, connect the volt meter and mod/battery, press the button of mod/battery, the currant volt will be shown on the screw. Another usage is,test the voltage when you vaping, connect the volt meter with mod/battery and 510 atomizers in two sides, you will see the voltage when you are vaping. But this way is not recommended, it may hurt your mod/battery.