# Exercise: Create a true ratio of units to area for each centre type

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The answer to the exercise will be included and explained if you attend the course listed below!

 Category ==> SSAS - tabular  (29 exercises) Topic ==> Measures  (3 exercises) Level ==> Harder than average Course ==> SSAS - Tabular Model
Before you can do this exercise, you'll need to download and unzip this file (if you have any problems doing this, click here for help).

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If you haven't already done so, run the SQL script in the above folder in SQL Server Management Studio to generate a database (not for commercial use or copying) called MAM

Again if you haven't already done so, create a new project called BaseModel, and import the following tables: tblAnimal, tblCentre, tblCentreType, tblPos, tblProduct, tblQuadrant, tblRegion, tblSpecies, tblStore, tblTown, tblTransaction.  Delete any measures already created.

Create the following measures:

Name What it shows
AverageMetres The average square metres area for the filter context.
AverageUnits The average number of units for the filter context.

This should allow you to create the following pivot table:

The average square metre area and number of units for each shopping centre type.

Create a measure called FalseAverage which divides the average metres by the average units, and show this in your pivot table:

The true average for any cell should be [the total square metres for that cell's filter context] divided by [the total number of units for that cell's filter context]

Now create a measure called TrueAverage which uses the AVERAGEX function to work out the true average ratio:

Notice that the figures are slightly different in each case.

The Shopping Centre row is returning an error because the Market Quay centre has 0 units (at least, according to the MAM database), so we're getting a divide-by-zero error.  To get round this, amend your true average to omit any centres where the number of units equals 0 to get:

The final figures: retail parks have much larger average unit sizes than factory outlets.

If you want to keep a copy of what you've done, use DAX Editor to create a copy of your measures with extension .dax called Dodgy stats, and save your workbook with the same file name.