Share | Price Direction Indicator (PDI) Calculator and Chart Maker Help Long Price Series: For long price series (many years of daily prices) there may be a delay of a few seconds before the results are displayed. When using daily prices for durations greater than five years, you may encounter a server error message. Because the total number of buy and sell combinations is equal to ((number of prices) * (number of prices -1 ))/2, long daily price series containing thousands of prices can require millions of computations causing the server to time out and send an error message. Therefore, use weekly or monthly prices for series more than 10 years long. Stock Symbol: Be sure to use yahoo! symbol naming conventions when you enter a stock symbol on the form. For example, enter ^GSPC for S&P 500 prices. If you enter an invalid code, the displayed results will be meaningless. See tables of Yahoo! Finance index symbols for U.S. and world markets. Valid Dates: Before you complete the calculator form, check the selected stock's first valid Start Date from historical prices at finance.yahoo.com. For example, Pfizer (PFE) price data begins on January 4, 1982. If you enter a start date that is prior to the start date for prices in the yahoo data base, yahoo uses their start date when returning prices. Yahoo! updates the daily closes a few hours after the stock market closes so if you run the calculator before the update, the effective prices will be from the previous trading day. Be sure that the End Date: is later than the Start Date: to avoid meaningless results. And the last date must be the current date or prior to it since there are no prices beyond the current date in the finance.yahoo price database.