From the Turtles:
The Turtles were instructed to decrease the size of the notional account by 20% each time we went down 10% of the original account. So if a Turtle trading a $1,000,000 account was ever was down 10%, or $100,000, we would then begin trading as if we had a $800,000 account until such time as we reached the yearly starting equity. If we lost another 10% (10% of $800,000 or $80,000 for a total loss of $180,000) we were to reduce the account size by another 20% for a notional account size of $640,000