“Unlike some of the true formulas, the 10% rule involves no value judgments or complicated calculations. Instead, the stockholder need only calculate the value of his account at each week’s closing price – something he might very well do in any case.”
“At the end of each month, the weekly figures are averaged and recorded. So long as the monthly average continues to rise or hold relatively steady, a fully invested position is maintained. However, when the average falls 10% below a previous high, all holdings promptly are sold.”