There are two ways of inputing voltage:7 batteries and DC3V direct current supply(AC100—240V), built-in LED source.
Each refractometer is coming with a bottle of 2ml refractive index liquid.(RI: 1.785±0.005) with unique design of the bottle(Proprietary technology ZL200620096730.7). We can't promise to send it as liquid is considered dangerous by airport.
It is much safer ,much economical and more convenient.