A special dialog is provided for the interpolated-series parameterisation of a time series, which consists of a variable number of period/value (usually year/value) pairs. It has two rows of periods and values, respectively, and the usual formula bar. However, only numeric constants are allowed.
STEM extrapolates as a constant value outside the range of periods defined, and interpolates linearly between them.
New values are added by first entering a Period and then entering a Value in the cell below. Periods are automatically sorted into chronological order.