If you want to count distinct values in DAX you have at least two ways of doing this. You can use the distinctcount or you can use countrows with distinct.

A sample can be viewed below

EVALUATE
SUMMARIZE (
    'Product',
    "Number of products version 1", DISTINCTCOUNT ( 'Product'[Product Id] ),
    "Number of products version 2", COUNTROWS ( DISTINCT ( 'Product'[Product Id] ) )
)

In MDX the same thing can be done using this code

WITH MEMBER CountDistinct
AS COUNT(DISTINCT [Product].[Product Id].[Product Id])

SELECT {[Measures].[CountDistinct]} ON 0
FROM [Internet Operation]

You also have a distinctcount in MDX that can be used.