I have 5% vlt tinting film that I cut to fit my lenses. I did this 10 times for each lense so the film overlaps each time. The formula (vlt1 * vlt2)100 = vlt3 is used to calculate the new vlt of the glasses. mine would be (0.05^10)100 = 9.765625e-12% vlt or 0.000000000009765625% vlt.