Picking up on "So that I can later calculate the integral . . ." you could do this in JSL using this kind of approach:
ames Default To Here( 1 );
// Example data
dt = Open("$SAMPLE_DATA/Big Class.jmp");
// Graph Builder with Smoother
gb = dt << Graph Builder(
Variables( X( :weight ), Y( :height ) ),
Elements( Points( X, Y, Legend( 6 ) ), Smoother( X, Y, Legend( 7 ) ))
);
// Save the Smoother formula! (see https://community.jmp.com/t5/Discussions/JSL-to-save-smoother-formula-from-Graph-Builder/m-p/417262#M66636)
gbb = Report(gb)[GraphBuilderBox(1)];
gbb << updateElement(1, 1, 2, {Save Formula});
// Get the saved formula from the table
form = Column(dt, "Smoother(height)") << getFormula;
// Make the independant variable 'x'
SubstituteInto(form, Expr(:weight), Expr(x));
// Integrate it between 80 and 140
area = Integrate( form, x, 80, 140 );
Print(area);
// Print area estimated 'by eye'
Print("Area estimate: "||Char(62.5 * (140 - 80)));