How to set a Reference Line on each page with Page option in Graph Builder?

[#1]

The following script plots some charts with the page option in graph builder? How to I set a horizontal reference line, for each chart, say at Weight = 80Kg and label it (80kg) using JSL?

(I need the reference line to remain even if there is a change in the number of charts plotted)

Names Default To Here(1); 
dt = open("$SAMPLE_DATA/Big Class.jmp");
gb = dt << Graph Builder(
	Size(528, 2954),
	Show Control Panel(0),
	Variables(X(:height), Y(:weight), Page(:age)),
	Elements(Points(X, Y, Legend(15)), Smoother(X, Y, Legend(16)))
);

[#2]

Names Default To Here(1); 
dt = open("$SAMPLE_DATA/Big Class.jmp");
gb = dt << Graph Builder(
	Size(528, 2954),
	Show Control Panel(0),
	Variables(X(:height), Y(:weight), Page(:age)),
	Elements(Points(X, Y, Legend(15)), Smoother(X, Y, Legend(16)))
);

axis = gb << XPath( "//AxisBox" );
Summarize( page = By( :age ) );
axis[2::(2*NItems( page ))::2] << Add Ref Line( 80, "Solid", "Red", "Reference" );

[#3]

@Mark_Bailey  Stops working for me (JMP 16.2) if I invoke Local Data Filter on Age after plotting, as below

[#4]

Easiest way is to add new column to your data table with same value for each of the rows and add that to your graph. This will work with filters

[#5]

@jthi your suggestion works fine, except that I would like the line label to be on the right. Is there a way to change the location of the line label?

[#6]

I don't remember which options are available in JMP16 as I'm mostly using JMP18 nowadays (with some JMP17 mixed in)

Names Default To Here(1);
dt = Open("$SAMPLE_DATA/Big Class.jmp");

dt << New Column("Ref", Numeric, Continuous, Set Each Value(80));

gb = dt << Graph Builder(
	Size(528, 984),
	Show Control Panel(0),
	Variables(X(:height), Y(:weight), Y(:Ref, Position(1)), Page(:age)),
	Elements(
		Points(X, Y(1), Legend(15)),
		Smoother(X, Y(1), Legend(16)),
		Line(Y(2), Legend(17))
	),
	Local Data Filter(
		Add Filter(
			columns(:age),
			Where(:age == {12, 15}),
			Display(:age, N Items(6))
		)
	),
	SendToReport(
		Dispatch({}, "400", ScaleBox,
			{Legend Model(
				17,
				Level Name(0, "Ref", Item ID("Mean(Ref)", 1)),
				Properties(
					0,
					{Line Label Properties(
						{Name Label(1), Name Label Position("Last")}
					)},
					Item ID("Mean(Ref)", 1)
				)
			)}
		)
	)
);

Write();

[#7]

No need to change the data table.

Replicating the axis setting via

Link Page Axes( "Y Only" )

copies the reference lines as well.

e.g.

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
Graph Builder(
	Link Page Axes( "Y Only" ),
	Variables( X( :height ), Y( :weight ), Page( :sex ), Overlay( :sex ) ),
	Elements( Points( X, Y), Smoother( X, Y) ),
	SendToReport(
		Dispatch( {}, "weight", ScaleBox,
			{Add Ref Line( 100, "Solid", "Black", "", 1 )}
		)
	)
);