I'm not sure what you are saying, Cee_Jay? Do you disagree with how I put it? [And where does
subtraction come into the picture?]
- Watts = Volts X Volts / Ohms
I just picked the simplest, most useful formulae for vapers' purposes: W = E²/R and I = E/R ... changing E's and I's to more familiar measurement names (and expressing Volts² as Volts X Volts, because I didn't know how to type ²

).
We
know (or are told by the manufacturers/suppliers) the battery voltage and atomizer resistance (ohms). What we
care about is the power or intensity of the
vape (measured in
watts) and the current (measured in
amps) that can fry our atomizer.