range = 1.7*crange;
    startheading=heading;startpitch=pitch;startrange=range;startcenter=center;
    viewer.camera.lookAt(center, new Cesium.HeadingPitchRange(heading, pitch, range)); 
///////////////////////////////////////////////////////////////////////////////////
<font class="button2"><b>Present Range </b> <span id="range_value"><script>document.write(Math.rount(1.7*crange));</script></span><b> Meters</b></font></td><td>
//////////////////////////////////////////
        gviewer.clock.currentTime =Cesium.JulianDate.fromIso8601("1900-01-01T00:00:00Z");
        gviewer.camera.lookAt(startcenter, new gCesium.HeadingPitchRange(startheading, startpitch, startrange));
        parent.SiteClick("Start");
/////////////////////////////////////////////////////////////////////////////////
<script>

document.getElementById("myRange").min=20;
document.getElementById("myRange").max=3*crange;
document.getElementById("myRange").value=1.7*crange;
function mySpareFunction() {}
/////////////////////////////////////////////////////////////////////////////////////////////////
<script>
    var slider = document.getElementById("myRange");
    slider.oninput = function() {
    console.log(slider.value);
    var this_heading=gviewer.camera.heading;
    var this_pitch=gviewer.camera.pitch;
    range=slider.value;
    gviewer.camera.lookAt(center, new gCesium.HeadingPitchRange(this_heading, this_pitch, range));
    document.getElementById("range_value").innerHTML = range;
}