DAX

Hi marsclone,

I had a test to calculate the difference based on the data as your descripted. Please check the following steps:

 1.Enter the data and new a Year column using the formula:

Year = YEAR(Table2[date])

2.Create three measures to calculate that you want.

ave 2017 = CALCULATE(SUM(Table2[Revenue])/SUM(Table2[qty]), FILTER(Table2,Table2[Year]=2017))

ave 2018 = CALCULATE(SUM(Table2[Revenue])/SUM(Table2[qty]), FILTER(Table2,Table2[Year]=2018))

difference = [ave 2018]-[ave 2017]

3.Then we can get the result as below.

For more information, please check the pbix as attached.

https://www.dropbox.com/s/rfdinx3zzxg9i5h/DAx1.pbix?dl=0

If the above DAX don’t help, please share sample data of your table and post expected result.

Regards,
Frank