A line chart can have either two dimensions and one expression or one dimension and N expressions. So you can create four expressions, one for each quarter, and an expression for your Plan value with only the PIT dimension. Or you can add a reference line on the Presentation tab. Since your plan value of .3 is static anyway over the PIT values that is the easiest solution. See attached example.
comm155719.qvw 152.2 K
Your first suggestion would work but means I'd have to create a separate expression for every possible interval; the real data will have months, quarters, years and combinations of these which should be selected by the user.
Regarding the second suggestion, I can't use the reference line because I want the user to choose from several (linear rather than constant) plan/target lines to include in a graph.
For example, the user might select a subset of the data (based on dimensions not shown in the sample file), specify 3 different quarters (e,g, 2013-Q3 to 2014-Q1) to display for that subset and then add a plan line that is most appropriate for the given selection.
Thanks very much for your help,
PS: This* is a QlikView limitation as opposed to a logical limitation, right?
* A line chart can have either two dimensions and one expression or one dimension and N expressions.