This is a parabolic sar of averages difference with alerts. What it does is measures the difference between price and the psar and draws the histogram accordingly. If price is far from the bullish psar then the histogram will be a thicker bullish color that is greater than zero, as the price gets closer to the psar, the histogram should reflect that by the histogram width being less, and maybe helping to get out of a trade in profit. The idea is the same for a bearish psar except the histogram is below zero in a bearish color.