By default, the HistogramUnitScale property is equivalent with ResizeUnitScale property. The HistogramUnitScale property defines the time-scale unit to determine the effort of bars with variable-effort (effort of expression/string type). The HistogramUnitScale / HistogramUnitCount property have effect only for item-bars with ItemBar(exBarEffort) property to refer an expression (defines an variable-effort). The value keyword indicates the date-time being queried, the start and end keywords specify the starting and ending points of the bar as indicated by exBarStart and exBarEnd fields in the ItemBar property. For instance, the exBarEffort on "weekday(value) in (0,6) ? 0 : 2", means that that effort to do the job is 2 for any day in the task, excepts the Sundays(0) and Saturdays(6) (weekend.

For instance, the "(hour(value) > 5 and hour(value) < 18) ? 2 : 0" indicates that the bar's effort is 2 for any hour between 6AM and 18PM, and 0 for rest.

The following screen show shows the correct histogram (HistogramUnitScale property on exHour):