Calculating difference between columns

hhdez ,Last Day Non Continuous day or tailing 7 should work in case you have date

example

Last Day Non Continuous = CALCULATE([sales],filter(ALLSELECTED('Date'),'Date'[Date] =MAXX(FILTER(ALLSELECTED('Date'),'Date'[Date]<max('Date'[Date])),'Date'[Date])))

or

Last Day Non Continuous = CALCULATE([sales],filter(ALLSELECTED('Date'),'Date'[Date] =calculate( max(Sales[Sales Date]), FILTER(ALLSELECTED('Date'),'Date'[Date]<max('Date'[Date])))))

7 Day behind Sales = CALCULATE(SUM(Sales[Sales Amount]),dateadd('Date'[Date],-7,Day))

Day Intelligence - Last day, last non continous day
https://medium.com/@amitchandak.1978/power-bi-day-intelligence-questions-time-intelligence-5-5-5c3243d1f9