What is the different between two modes of iStick TC40W?

iStick TC40W has two kinds of modes, which are temperature control mode and variable wattage mode. The range of temperature is from 200 – 600° F and 100 – 315° C, and the range of variable wattage is from 1-40 watts. In variable wattage mode, it allows the mod fire coils from 0.15 – 3.6 ohm, and in temperature control mode, it’s capable of firing nickel coils with resistances of 0.05 – 1.0 ohm.