Add test number column based on different column value changes

[#1]

I have a data of a parts that are being tested on different test tester. If part fail on it won't be tested on next stations. I like to add a column to track the test number.

[#2 · Accepted solution]

Here is how I would approach the problem with this formula for the column

As Constant( val = 0 );
If( Lag( :Serial Number ) != :Serial Number,
	val = 0
);
If( :Tester == "Tester 1",
	val
	++);
val;

[#3]

Thanks Jim