Oa series, the cells between the first and last cells in the series must be blank.

To interpolate a series, the cells between the first and last cells in the series must be blank. Interlocation is the process of producing a time series at a higher frequency than is actually available, for example a monthly seres from quarterly data. To calculate a series of values from a starting point without a defined ending point, you have to extrapolate the values. When you extrapolate a series, the step value represents the amount that each value is increased or multiplied as the series is extended. 

If the experiment was perfomed more then once and you get the same results