The Sampling Interval on the Time tab of the iHistorian Edit Source dialog box allows you to select the type of sampling as either a time interval or number of samples. If you select Interval, the time interval for sampling can be set in the Data Point Interval section. If you select Number of Samples, the window changes so that you can specify the total number of samples.
For interpolated/calculated retrieval modes, an interval is derived from dividing the number of samples into the configured time span. The resulting data set will contain samples that are evenly spaced within the time range defined by the start time and end time for most sampling modes.
For the retrieval mode Raw by Time, you cannot specify the data point interval nor the number of samples. Raw by Time displays all raw samples of all qualities with a timestamp greater than the start time and less than or equal to the end time; therefore, you only need to set the start time and the time span.
For the retrieval mode Raw by Number, you can set only the start time and the number of samples because this type of retrieval mode displays all raw samples of all qualities with a timestamp greater than or equal to the start time (the end time is ignored). The number of samples specified, therefore, determines the maximum number of values to retrieve.
For more information about setting the data point interval, see Data Point Interval and the Retrieval Mode.