Cell permeability by FLOW CYTOMETRY

[dino]

Hi,
I would appreciate it if anyone could help me with this.
Here's the deal:
I am a beginner FACS user. I have a FITC-coupled molecule that passively enters cells (permeability). I tried to quantifiy the minimum concentration at which the drugs penetrates the cells and how much time it needs so I did 3 timepoints (5, 15 and 60 min) and several concetrations (from 1nM to 100 µM).
I used the same pop for all conditions and set the fluorescence therhold to be at the maximum autofluorescence of the non treated (control) cells.
I noticed that 2 parameters are increasing with the concentration of the FITC-molecule: the % of fluorescnent cells (as expected!!) and the "Mean". What does "mean" stand for? Is it the the mean of fluorescence per cell? And is the corresponding SD indicative of the reange of fluorescence of my cells?
If the answer to the above is "yes", does it mean that, besides knowing how many cells take up the molecule, I can do a relative quantification of the amount of molecules that get in each cell?

THANKS!