Help with pivot calculated fields?

I am attempting to add a calculated field to my pivot table. The field calculation has to be 1-Sum(pivottablefield)/Count(pivottablefield). This does not work as i thought it would. The sum function works just as it does on the pivottable itself. If i create a calculated field of just SUM(field) it will give me the same results as if i added my field and told the pivot table to display it as sum. The count field on the other hand does not work as the pivot table does it and just gives me straight 1's all the way down for my data points. That does not help me get a very good average.. all of my results appear as negative numbers. Is there a different function name i could use in my calculated field to better replicate the count function of the pivot table?

guessing this cant be done?