A time series specified as an Interpolated Series consists of a number of period/value pairs. STEM provides a special dialog with rows for periods and values respectively, and a formula bar, similar to normal data dialogs.
Figure 1: Interpolated Series dialog
Periods are automatically sorted into chronological order: values are interpolated linearly between these periods, and extrapolated as a constant outside the range of periods given.
Figure 2
below indicates how an Interpolated Series is interpreted. If you specify year/value pairs for 2001 and 2006, the remaining values are calculated as shown.
Figure 2: Interpolated Series interpolation & extrapolation