Custom Measures versus Custom Report Expressions

The decision to use a custom measure versus a custom report expression depends on how you want the data to be computed.

Custom Measures

A custom measure is a new measure you create from fields in the underlying database, using a special formula syntax in the Admin > Customize Space > Custom Measures tab. When you add a custom measure, Designer and Visualizer list it in their Default Subject Areas.

For example, a custom measure called Revenue Formula shows total revenue using this formula:

[Quantity]*[Unit Price]

Birst multiplies each unit price with its corresponding quantity and then sums it.

Report Expressions

Custom report expressions are expressions that are presented to the user on-the-fly in a report. They use measures from a subject area. The aggregation is included in the definition of a measure to be used on a report.

For example:

[Sales Date: Sum: Quantity]*[Sales Date: Avg: Unit Price]

Differences Between a Custom Measure and a Report Expression

Compared to the custom measure that calculates from the database fields, the report expression gives a different result because it first computes the aggregations. For example, it computes the sum of Quantity and then multiplies that with the average Unit Price for all units.

Note: It is very important to be aware of this difference if you want accurate data.

This example divides the revenue into product categories and the result differs from the custom measure approach:

Table 1. Result Comparisons
Category Name	Sales Date:Revenue Formula	Sales Date:Sum:Quantity
Fruit	31,295.48	31,262.89
Meat	83,303.36	83,078.7
Nuts	45,370.75	45,329.71
Vegetable	24,427	24,537.05

For this example, the first approach would be the most correct; however, the approach you choose may vary based on what you are trying to communicate.