Need Help Calculating Book Value (Adjusted Cost Base) of Investments

Thanks Milan, that formula works well and solves the account instance issue I was having. However, the main issue I am having remians: the book value is not calculating properly and I am getting a circular dependancy error whenever I try to calculate it. This is because the book value calculation for redemptions depends on the previous BVPS, which depends on earlier ending book value calculations. Do you know if there is any way to get around this?