Hi LC, I did this based upon the long term P/L of the investment. I started it in about 1998, so didn't have too long a track record to track. The P/L showed my costs to that point. I divided the costs by the number of shares owned at that time to come up with a current cost per share and then added 10%, I believe.
So, at about 10% above the ave. cost/share I started to sell and recover some cash.
I did this on a couple of other holdings as well. Some, of course needed to rise significantly before we reached that first 10% profitable sale.
Best regards, Tom