Value 7 days earlier than selected

You have to change the filter in your expression

DAY - 7 =

CALCULATE (
    COUNT ( 'public Measurement'[result] ),
    FILTER (
        'public Measurement',
        'public  Measurement'[DAY]
            = DATEADD ( SELECTEDVALUE ( 'public Measurement'[DAY] ), -7, DAY )
    )
)

I have a problem with the type of parameters in and I don't know how to deal with it

Hi Zbig62 

I don't think you should use the “DAY” field in the "public Measurement" table as a slicer, please create a calendar table to use as a slicer. And don't create a relationship between the calendar table and the "public Measurement" table.

1. Create a calendar table and use it as a slicer.

Calendar = DISTINCT('public Measurement'[DAY])

 2. Replace the field “DAY” in your measure with the field “DAY” of calendar table.

DAY - 7 = 
CALCULATE(
    COUNT('public Measurement'[result]),
    FILTER(
        'public Measurement',
        'public Measurement'[DAY] = SELECTEDVALUE('Calendar'[DAY]) - 7
    )
)

Here is my simple test result:

By the way, when the day DAY-7 does not exist for the "DAY" in your data, the measure will return blank. For example, if you slicer selects 2024-02-01, DAY-7 is 2024-1-25, because the data for 2024-1-25 does not exist in your table, the measure returns blank.

Best Regards,
Jarvis Tang
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

Sorry I didnt realise that Dateadd function needs an exclusive date table.Your approach wouldnt work as you are trying to compare rows within the current row context and subtracting from the same value using a filter.

As suggested by Anonymous you need a date table. You can use the solution provided by Anonymous