The 4^{th} parameter is useful when **referencing out of range** in relation to the dataset that has been defined for the crosstab at hand.

This will normally result in the error message “*not defined*”. By using the 4^{th} parameter you can insert a numeric value which will replace the error message.

An example:

- Create a new analysis
**Monthdifference**with a crosstab showing**Revenue****per****Time Hierarchy (Month)**. - Add a calculation showing the
**difference between current month and the previous month**.

The formula could be: **sum(d1, 0, m1) – sum(d1, -1, m1)**

In this particular case this formular will return “*Undefined*” in the first row – because there is no previous month in the dataset – and the reference is out of range.

In this case the 4^{th} parameter can be a solution.

New formula: **sum(d1, 0, m1) – sum(d1, -1, m1, 0)**

The last 0 indicates that the **value 0 should be inserted** in case of **reference out of range**.

Now the first row (January) is calculated as if the previous month was 0.

## Comments

Ashwini SayaniHi, improving on this example - how do I calculate the difference between prev month this year and prev month last year please?

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