Parabolic SAR

Parabolic Time/Price System is used to produce BUY and SELL signals after trend reversal. It can produce trailing price stops and is usually referred to as the "SAR" (stop-and-reversal).

Parameters:

1. AF_min - minimum value of averaging constant.
2. AF_max - maximum value of averaging constant.

Calculation:

The indicator is calculated differently in case of BUY and SELL signals. The initial SAR value is set to the minimum price in the previous time period for BUY signals, it's set to the maximum price for SELL signals. In the very first interval the SAR value is set to the maximum price in that interval and SELL signal is assumed. The acceleration factor AF is set to  AF_min .

Then SAR is calculated:

When the price reaches a new minimum or maximum in the trend direction, the exponential averaging constant AF is increased by  AF_min  compare to its value in the previous period. AF is increased until it reaches  AF_max .

The calculation restarts when the price crosses SAR level.