Trying to calculate miles driven:
Mileage Driven = IF(
ISFILTERED('Mileage Tracker'[Month]),
ERROR("Time intelligence quick measures can only be grouped or filtered by the Power BI-provided date hierarchy or primary date column."),
VAR __PREV_MONTH =
CALCULATE(
SUM('Mileage Tracker'[Odometer Reading]),
DATEADD('Mileage Tracker'[Month].[Date], -1, MONTH)
)
RETURN
Divide(
SUM('Mileage Tracker'[Odometer Reading]) - __PREV_MONTH,
__PREV_MONTH
)
)