With all Vv / Vw APV's you can choose watts or volts, you are either in watt mode or voltage mode, one or the other not both at the same time.
Whichever you adjusted or checked last is the mode you're in.
The point in owning a variable power device is being able to vary the power to find your own personal 'sweet spots' using a wide variety flavors, pg/vg ratio's, and resistance of delivery device.
Pick watts or volts, start off at a low setting and gradually work your way up in power taking a vape or three at each setting until you find what you're looking for in vape quality. If you get a hint of burnt taste turn it down a little.
Vaping is all about personal preferences, power settings are just another variable of individual / personal preferences, there are no best or optimal power settings.