Calculating variance per location

Hi, I'm fairly new to Power BI and DAX. I would very much appreciate the help. Thanks in advance.

I have a database with accidents and incidents, the location where they happened, the month they happened and the reference. I’m trying to calculate the variance in the same way as I do in excel. In excel the grand total is the number of times a location is counted in the data in the current month. A separate tab counts the location listed in the previous month. Variance is then calculated by subtracting the previous month from the current month.

In PowerBI the location is counted by counting the reference (string value) per location. I’ve tried to make measures for the count per location in the current month and the previous month and another measure for the difference (variance). Unfortunately it takes the total and shows that for every location.

I’ve made the following measures:

Count_reference = COUNT('Data'[Reference])

current month = CALCULATE ([Count_reference], FILTER (ALL ('Data'), 'Data'[Event Month]= DATE (YEAR (TODAY ()), MONTH (TODAY ())-2, 1)))

previous month = CALCULATE ([Count_reference], FILTER (ALL ('Data'), 'Data'[Event Month]= DATE (YEAR (TODAY ()), MONTH (TODAY ())-3, 1)))

monthly variance = [current month]-[previous month]

Is there a way to calculate the variance per location in this specific set of circumstances?

Please find the excel file here:

https://www.dropbox.com/scl/fi/o6928pmqfqahcc1lthc3z/Accidents-and-Incidents-Dummy.xlsx?dl=0&rlkey=6q760jl9t5anpbzsib1525sap