The Lasso feature is new in version 6.13 - it allows you to select points on your Scatter chart and highlight them. There are a number of properties that are available to you that allow you to customise that appearance and how the feature behaves (for example a callback function so that you can integrate it into your existing code along with persistence, custom persistence load/save functions and appearance customisation).
<?php

 */
include_once "environment.php";
use phpRGraph\rgraph_chart;
use phpRGraph\rgraph_options;

// rgraph chart
$template = "demo_lasso.php";
$draw_option = "draw();";
$width = "650";
$height = "400";

$chart = new rgraph_chart("cvs", null, "Scatter");


$x_values = array(156,157,159,160,161,162,165,170,170,171,172,173,173,177,178,184,188,189,190,194,196,200);
$y_values = array(162,160,162,159,162,170,166,170,167,169,174,173,176,173,178,180,188,182,185,193,190,196);

for ($i=0; $i<count($y_values); $i++)
{
   $color[$i] = "blue";
   $tooltip[$i] = "Body Size: "  . $y_values[$i] . "cm 
Arm Length: " . $x_values[$i] . "cm"; //$tooltip[$i] = "Körpergrösse: " . $y_values[$i] . "cm
Armlänge: " . $x_values[$i] . "cm"; } $data = $chart->createScatterData($x_values, $y_values); $chart->set_data($data); $options = new rgraph_options("default.ini"); $options->set_option("marginLeft", 100); $options->set_option("marginRight", 10); $options->set_option("title","Body Size versus Length of Arms"); $options->set_option("lasso", true); $options->set_option("lassoPersist", true); $options->set_option("lassoPersisLocal", true); $options->set_option("tickmarksStyle", 'circle'); $options->set_option("tickmarksSize", 6); $options->set_option("title","Body Size versus Length of Arms"); $options->set_option("xaxisScale", true); $options->set_option("xaxisScaleMin", 150); $options->set_option("xaxisScaleMax", 200); $options->set_option("yaxisScaleMax", 203); $options->set_option("yaxisScaleMin", 150); $options->set_option("yaxisScaleUnitsPost"," cm"); $options->set_option("yaxisTitle","Body Size"); $options->set_option("xaxisTitle","Length of Arms in cm"); $options->set_option("xaxisTitlePos",0.50); $options->set_option("yaxisTitlePos",0.50); $options->set_option("trendline", array(true)); $options->set_option("trendlineColors", array("red")); $options->set_option("trendlineClipping", false); $chart->set_options($options); $rgraph_json = $chart->toPrettyString(); $chart_name = "scatter"; $event_script = ""; $chart_script = ""; include_once ($templates . $template); ?>