Row difference (moving range)

[#1]

Hello,

Can you help how to write a formula for row difference? My problem with the formula is that I have a variable column "Partnumber" and I don't want the row difference calculated if the next row has a different partnumber than the current row. Please find a sample table. In row number 30, the part number is different than the previous row. For row 30, I don't want the calculation but then continue as long as the next rows
 have the same part number as row 30 and so on.

[#2]

I think an if statement will do what you want, see the column formula below.  This will return zero for row 30, you might prefer a missing value.

If( :Epi_Product_Number == Lag( :Epi_Product_Number, 1 ),
	Dif( :"Mean(Average)"n ),
	0
)

[#3]

thank you very much. It worked very well.