Prior High and Low - The amount of excess at the prior high and low of the trading session.
TPO -Time Price Opportunities, Each half-hour of the trading day is designated by a letter. When a certain price is traded during a given half-hour period, the corresponding letter or TPO is recorded next to the price.
Excess is being defined as the amount of single wide TPOs at the high and low of the day. See the image below for an example.
