Standard Deviation that factors in the amount of sales needed in Excel 2002

Hello,
I am attaching a workbook that I was wondering if someone could help me complete. I am a newbie and I have been researching the boards to come up with solutions which got me this far.

I hope that I could explain:

The data attached has a listing of the employees who had more than 15 recorded sales per month. I calculated the averages and standard deviations for each category (these are listed on the tab labeled "Averages STDev").

Once I had those figures calculated I had the information necessary to standardize the data. The common formula for standardizing is "employees figure" minus "average figure" divided by the standard deviation for the category.

The end result is a figure that tells you how many standard deviations above or below average the employee is. Since all categories then become represented as standard deviations above or below average, I am able to combine these figures for a composite score at the far right of the worksheet. The only thing that this method does not take into account is the amount of sales that each employee does.

The concept I would like to know with this is if the total office average gross sales is $2,800 and 2 employees have $2,500 averages but one does 20 sales a month and one does 40, then the employee who does 40 should have a (slightly) higher score than the adjuster who does 20.

I hope this makes sense if someone could enhance what I have already done and if there is a way to also chart each employees stats.

Thanks in advance!