If you re-build then you MUST HAVE A WAY OF CHECKING YOUR OHMS ..
Ohms law is essential knowledge before you press the button on your mod for the first time.
Many accidents occur when a short is present and sometimes with disastrous results .
These meters read the coil that you want to use and gives you the information you need to complete that formula, just as long as you know the amp limit of the your battery.
BETTER SAFE THAN SORRY