So using that formula you gave me, using the following data (im adding a 'key' at the end - just as a point of reference) :
BCLog
100, 400, Bananas, 1
401, 500, Apples, 2
501, 700, Bananas, 3
BCUsed
105, 200, Bananas, 1
It is pointing that BCUsed entry out because it is less than entry '3' on...