Measure Names are not accessible in calculated fields. Here is a proposed idea that deals with that. You may want to vote it up: http://community.tableau.com/ideas/1071
Can you reshape your data so that you use a dimension in the columns? For example [Grade]
Thanks for the quick reply. Do you mean reshape the data so that each school appears many times with a column that indicates the grade that the test score column reflects? Once I do this, are you sure I be able to achieve the custom reference line?
Is your data at the school level? If so, yes by having multiple records per school (one for each grade) you could use Grade as a dimension.
SCHOOL GRADE SCORE
A 3 90
A 4 91
A 5 87
B 3 89
B 4 86
B 5 87
What I had in mind is that you would use the dimension (GRADE) to set a calculated field along the lines of what you outlined on your first post.
I put together an example using the Superstore datasource. This uses the Department as the the dimension for the columns. See attached.
custom_reference_line.twbx.zip 931.3 KB