This product has an AC voltage of 220V input and output, and can only be reduced in voltage. It can only be adjusted when connected to a load. It is useless to connect it to a multimeter without load, not a transformer. Please read all the instructions on the product page before placing an order. Specification parameters: Product name: 4000W AC voltage regulator, Thyristor model: BTA41600B, Size: length 85 * width 55 * height 38mm, knob inner hole 6mm, Maximum power: 4000W resistive load limit power, power should be reduced for long-term use. Efficiency: Over 90%, Working voltage: AC 220V, Voltage regulation: AC 10-220V. Note that the load must be connected first before voltage regulation. Controllable silicon is mainly used for resistive loads such as electric heating filament incandescent lamps. Most single-phase AC motors can also be used, but it is not guaranteed that they can be used. For other types of loads, please confirm by the buyer.