Why does the ALL function fail in this case?

Hi Chris123Terr ,

Please try:

MEASURE = CALCULATE(SUM('table'[Duration]), ALLEXCEPT('Calendar','Calendar'[TRIMESTRE]))

Or:

MEASURE = 
VAR _total =
CALCULATE(SUM('table'[Duration]), ALLEXCEPT('Calendar','Calendar'[TRIMESTRE]))
VAR _max = CALCULATE(MAX('Calendar'[Month Number]),ALLEXCEPT('Calendar','Calendar'[TRIMESTRE]))
VAR _month = MAX('Calendar'[Month Number])
VAR _result = IF(_max=_month,_total)
RETURN
_result

ALLEXCEPT - DAX Guide

Best Regards,
Gao
Community Support Team

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