Graphic Lines script

You would want to settle on a measurement unit, so if you want to use Millimeters, set the length of the line in millimetrs rather than inches—30" = 762mm

You create a line by adding it to the page. In my example the lines are getting added to the activePage—my p variable:

var p = app.activeWindow.activePage;

The position of the line is set via the geometricBounds property, which is an array of 4 points [y1,x1,y2,x2], so a 3rd vertical line could be added as:

var vLine2 = p.graphicLines.add({geometricBounds: [148,170,148+l,170]});
vLine2.properties = lp;

Here the units are millimeters:

app.scriptPreferences.measurementUnit = MeasurementUnits.MILLIMETERS;
var doc = app.activeDocument;
var p = app.activeWindow.activePage;
var l = 762; //30" as millimeters
var xy = 100 
var lp = { 
    strokeColor:"Black", 
    strokeWeight:1, 
    strokeType: "Dashed",
    strokeTint: 30,
    strokeDashAndGap: [4,4],
    strokeAlignment:StrokeAlignment.CENTER_ALIGNMENT
    }

var hLine = p.graphicLines.add({geometricBounds: [xy,0,xy,l]});
var vLine = p.graphicLines.add({geometricBounds: [0,xy,l,xy]});
hLine.properties = lp;
vLine.properties = lp;

//X: 170mm, Y: 148mm?
var vLine2 = p.graphicLines.add({geometricBounds: [148,170,148+l,170]});
vLine2.properties = lp;

app.scriptPreferences.measurementUnit = AutoEnum.AUTO_VALUE;