Some formulas require you to define a window length.

Let’s take as example the formula for a rolling mean:

Mean(series, window)

The window length you should input is the* number of observations* over which the function will be calculated. The number of observations is based on the frequency of the document.

Instead of typing a number, you can also use other formulas to get the number of observations in a specific time period, such as *YearLength()* or *QuarterLength()*.

For example, you can calculate the one year rolling mean of a series, by using the following formula:

Mean(series, YearLength())

The advantage of this formula is that you do not have to focus on the frequency of the document to decide what should be the number of observations.