Use Slicer selection in calculated column (Parameter)
<p>I have: 
- a slicer with dates and a table 'Log' with a column 'Date' with dates and a column 'Max' with numbers (e.g. 0,31)</p>

<p>I need to calculate the average of all values in the column 'Max' when the date is before the slicer selection date - and an average for after.</p>

<p>End result: a Card visualisation with the average of all values before the selected date and a Card visualisation with the average of all values after the selected date.</p>