Visual showing historic data as well as sliced data

[nick9one1]

I have a visual that shows bookings for the 'Academic year' selected in the slicer. 

I would like a second line on the visual that displays the bookings for the previous avademic year (2021-2022). 

The same table holds both sets of data. 
the Y axis measure is currently 

Booked Rooms = 
CALCULATE (
    COUNTX ( 'Lettings FACT_Lettings', 'Lettings FACT_Lettings'[LettingsFactKey] ),
    FILTER ( 'Lettings DIM_ReservationType', 'Lettings DIM_ReservationType'[ReservationTypeKey] = 1 )
)

The table has a column for 'academic year' and 'previous academic year'

[nick9one1]

does anyone have any suggestions?

[lbendlin]

Please provide sample data that covers your issue or question completely, in a usable format (not as a screenshot).
https://community.powerbi.com/t5/Community-Blog/How-to-provide-sample-data-in-the-Power-BI-Forum/ba-...
Please show the expected outcome based on the sample data you provided.

https://community.powerbi.com/t5/Desktop/How-to-Get-Your-Question-Answered-Quickly/m-p/1447523

[nick9one1]

The problem is that the slicer reduces the dataset the the selected academic year. 
So If I select 22-23, it displays the correct data, but any data from the previous year (21-22) is not available as it is filtered out of the dataset by the slicer. 

[lbendlin]

ok. What have you tried and where are you stuck?