Voltage is one of the factors that effects the amount of vapour you get. The greater the voltage, the higher the temperature, meaning more vapour.
Original, Logic CURV, Logic PRO and Logic Compact all have fixed power settings - 3.7 Ohm.
Logic LQD is an open tank device that allows you to select from two power settings high (4.2P Ohm) and low (3.7 Ohm). This allows you to customise your vaping experience.