The results returned by the algorithm do not depend on the quality of the data. You can choose to filter the data on quality using the Qualities combo box in the Edit Source window (see Configure a Trace)

Take care with End and End Last Historic Algorithms used on clients, or with ClearSCADA features, that run in Local Time with Daylight Saving Time. Ensure that the start and end times specified for the sample interval do not coincide exactly with the time at which the clock jumps backward. Include a small offset in the sample time, to offset the calculation to avoid the sample end or start time exactly matching the time that the clock jumps backward at the transition from Daylight Saving Time to Standard Time. A small offset of 1s or even 1ms should suffice. For more information about Daylight Saving Time, see The Effects of Daylight Saving Time Adjustments.