Hi Ed,
With mechanical mods, your wattage is dependent upon the resistance of the atomizer. For example, with a freshly charged battery putting out 4.2 volts, if you have a 0.8 ohm build, you're going to be vaping at 22.05 watts. With the same voltage, if you have a 0.5 ohm build, you'll be vaping at 35.28 watts.
We urge everyone working with RBA's and RDA's to use an ohm meter, and the Omnitester also measures output voltage.
http://www.smoktek.com/Smok-Omnitester--Digital-Ohm-Voltage-Tester_p_1058.html
Thank you,
Brad