Count all values in table that share same value as current row in pivot table

 have found a solution to this.

Step 1)

Go into main table query, remove any errors from the net value column (optional)

Create key from relevant columns

Close and load (to data model)

Step 2)

Duplicate this query

Use group by to get a row count using the key as the group category.

Close and load (to data model)

Build a relationship with the original table

Step 3) Use related to get the count column in order to use a 'downstream' variable in any Power Pivot Table (optional)

Thanks for your support peeps!