Like Session Volume, Session Volume HD shows the volume of transactions at different price levels, but Session Volume HD will automatically adjust the level of detail as you zoom the chart's scale. When you zoom in on a chart, the level of detail increases.
While the number of price levels must be configured manually in the Session Volume's settings, Session Volume HD calculates the number of levels dynamically. When fewer bars appear on the chart, more levels are displayed.
When calculating the indicator, the volume of bars with the lowest possible resolution is used. That resolution depends on the chart's time interval and is selected from a list of the following: 1, 5, 15, 40, 60, 240 and 1D, so that ~5000 bars fit into the interval.
For all second resolutions, the histogram is based on the volume of 1S bars.