Highest Value / Circular Reference Help
 

I use a spreadsheet to track stock portfolios and determine stop orders. I
place the Stop Orders every 30 days. To determine the Stop Order Price, I
need to take the highest value of either (1) a certain percentage (say 15%)
of the cost basis, (2) a certain percentage (say 15%) of the current value,
or, (3) the last stop order price. Since stock prices fluctuate, the "last
stop order price" could be higher than "15% below the current value", but I
can not set it up to automatically track the highest value without creating a
circular reference. Following is a shortened version of the spreadsheet:

Column A is a certain percentage below the current value.
Column B is a certain percentage below the cost basis.
Column C is where I have the problem. I need this cell to keep track of the
highest price that was ever reached when I update the spreadsheet. I need to
create a "watermark", as the current value fluctuates.
Column D has the formula to take the highest value of Column A, Column B, or
Column C, which creates my circular reference.

As I update the current values monthly, I have just been copying the values
from Column D (Highest value of A, B, & C) to keep track of this. I know you
can allow circular references, but is there any other way to keep track of a
highest value or achieve what I am trying to?

I can give more info if needed.