Calculating measure

Add new column in your table and o get sum of the average, something like this:

my average column = 
var myItem = myTable[Item]
var myCount =  CALCULATE(COUNT(myTable[Item]), FILTER(ALL(myTable),myTable[Item] = myItem))
var mySum = CALCULATE(SUM(myTable[Sale]), FILTER(ALL(myTable),myTable[Item] = myItem))
return DIVIDE(mySum,myCount,0)

try this and see if this works. We would have done it in few lines but try to be more detailed.

we can add another column for count as well.

Thanks,

P