Questions regarding pie chart

Hi

I want to show how manye percentage one value is of antother value. So I want a pie chart, where the full pie is a value of 1000 and then add another value, lets say 900, that shows how many percentage it is of the 1000. If I add them to a pie chart now the full pie will be 1900 because I add the sum of both values.

I really hope it makes sense. 

BR

Hans