New user needs help with DAX

Hi, KrilleGTI 

Based on your information, I create a table

Then I create a new measure named Average value by date

Based on your requirements, I've created a measure, and here's a preview of me

Here is my DAX

Measure = var a=MAXX(FILTER(ALLSELECTED('Table'),[Date]<MAX('Table'[Date])),[Date])

var b=CALCULATE([Average value by date],'Table'[Date]=MINX(ALLSELECTED('Table'),[Date]))

RETURN DIVIDE([Average value by date],b)-1

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Best Regards

Yongkang Hua

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