I want to display this value as a percentage, but I cannot change it from modeling (it's greyed out). It is already in percentage form in the query.
Measure =DIVIDE ( SUM ( Dump[Open] ), SUM ( Dump[Close] ), 0 )
share the dax measeure which your using
I computed the value on Kusto directly, it's displayed as 0.XX now.
I've used this method to format % or other custom units for a card.
Measure = ROUND( [Value] , 2 ) & "%"