The Horizontal Progress Bar can be adjusted by clicking on it. When adjusting is finished the onadjustend event fires. If you attach a function to the onadjustend event (as below) you can get the new value by looking at the .value property (eg myProgress.value).
<script> window.onload = function (e) { var hprogress = new RGraph.HProgress('myc', 83, 100, 0); hprogress.Set('chart.color', 'green'); hprogress.Set('chart.adjustable', true); hprogress.Set('chart.margin', 5); hprogress.Set('chart.tickmarks.inner', true); hprogress.Set('chart.tickmarks.zerostart', true); hprogress.Set('chart.units.post', '%'); hprogress.Draw(); RGraph.AddCustomEventListener(hprogress, 'onadjustbegin', function () {console.log('Old value: ' + hprogress.value );}); RGraph.AddCustomEventListener(hprogress, 'onadjustend', function () {console.log('New value: ' + hprogress.value );}); } </script>