At times, you may want to create a new item that depends on the values of other items in a column of data; these are called item-based calculations.

For example, suppose we create a calculation for the (average) vertical jump difference between two successive years. To do this, in the following visualization, we can select an item on which we want to base the calculation. In this situation, we are viewing a visualization on How do the values of vertical compare by year? so we can simply click on one of the vertical bars and then click Create calculation:

Next, in the calculation popup (shown here), we enter a name for our calculation:

After entering the name (VerticalDiff) to be used for the calculation name, we can leave 1999 selected as the first parameter, then change the addition (+) to a subtraction (-), and finally, select 2000 as the next parameter and click Done.

At this point, Watson Analytics creates the calculation as a new item and it appears in the visualization! To edit the calculation, click on the new item that is based on the calculation and then click Edit calculation, then click Delete.