[RedRiver]

The 720 Rule is: 720=ASF x minutes / mils. Where; ASF is Amps per square foot, mils is the desired coating thickness (1 mil = 0.001"). Therefore to solve for the duration in minutes the formula must be rearranged into the following : Minutes = 720 * mils. / ASF

Example : Solve for duration at 12 ASF and a 1 mil thickness.
This is how I would solve for the duration using my formula.
Minutes = 720 * mils / ASF
Minutes = 720 * 1 / 12
Minutes = 720 / 12
Minutes = 60


Do you notice the difference between my formula and your own?
Minutes = ASF/(mils * 720)
Minutes = 12 / (1 * 720)
Minutes = 12 / 720
Minutes = 0.01666

Now...Assuming that you made a type-o when presenting your forumla I will try to explain what may cause thinner thicknesses. (As to how I understand it).

One should consider ALL of the factors. The 720 rule is the formula used to calculate the anodizing duration and/or the projected outcome and it assumes the following : that your electrolyte is maintaining a constant temperature of 68F, that the electrolyte's concentration is exactly 9.4% H2SO4 by volume, that your surface area is calculated to the exact square inch and that you are utilizing an anode:cathode ratio of 3:1. Other factor such as alloy may have an effect on your results as well. Without meeting the exact specifications you will find some variation in your results. If what you suggest is true and that you are only achieving 7% of the expected thickness I would hazard to guess that your acid concentration is too high or your CD too low. It would seem that your anodic layer is being dissolved almost at the same rate as it is grown. Either that or you did not make a type-o when presenting your formula and you are anodizing for far too short of a duration.

Just out of curiousity, plug some numbers into your formula to give us an idea of what you're working with...It may help.

I hope this helps clear up the mystery somewhat...
- Dan