Here is how we use Ohm's Law for mech mods:
E=I*R
This is the equation where E=volts, I=Amps, and R=resistance
We always use 4.2 volts for the voltage as that will provide the max current draw on the battery as we don't know how much the battery voltage will sag and the voltage drop of the mod/atty combo.
We don't know how much current (Amps) will be drawn, but we do know the voltage and the resistance, so we use the equation to solve for current.
I=E/R
What I did is divide both sides of the equation with R. R/R=1 so we can throw that away leaving just E/R=I Now let's throw some numbers in there.
I will use 1 Ohm for resistance and 4.2 volts for the voltage.
I=4.2/1 so I=4.2 Amps
To find the lowest resistance you should use with a battery works the same way except you solve for R.
R=E/I
Here you would use the CDR for the current of the battery and 4.2 volts.
Using some numbers let's use 20 Amps for the battery and 4.2 volts.
R=4.2/20 R=0.21 so a 0.21 Ohm coil would be the lowest coil you should use with a 20 Amp battery.
Figuring power (Watts) works the same way.
P=I*E
is the equation where P=power (Watts) and I=current and E=volts
Using the same numbers from above
P=4.2*4.2 so P=17.64 Watts
If you didn't figure the current previously you can use this equation:
P=E*E/R and get the same result.
What I did there is substitute E/R for I
This is just simple Junior High School Algebra.