Hi Spencer,
In DAX, the first argument in CALCULATE() function is same as a measure, which means it should be aggregation on column, so you need to use aggregation function (like SUM).
Internet Previous Quarter Margin:=CALCULATE(Sum([Internet Total Margin]),PREVIOUSQUARTER('Date'[Date]))
And make sure the dates in date column is continuous. Since it just show BLANK() instead of error, please also check if it contains data one quarter ago.
Regards,
Simon Hou
TechNet Community Support
