The fourth expression is written as (COLUMN(2)-COLUMN(3))/COLUMN(2). Here, we pick up the column numbers instead of the actual field names for our calculation.

We can also write the expression in the following manner:

([WTD]-[Previous WTD])/[WTD]

We will get a bad field name ([WTD]-[Previous WTD])/[WTD] at the bottom of the Expression editor window. But don't worry, as Qlik Sense will still interpret the results correctly. This chink may be ironed out in future releases of Qlik Sense.

The expression does not make use of the fields that we have loaded into the application's data model. It instead uses the expression labels we have already created for the previous calculations. This is always a best practice option if you need to use the same calculation in the same table more than once. It make things simpler; you only have to change something once and, best of all, it is optimized and the calculation is already cached in RAM.