side by side map compare

Hello,
i want to compare 3/4 maps side by side in cesium like this:
http://tools.geofabrik.de/mc/#15/49.0091/8.4092&num=4&mt0=mapnik&mt1=google-map&mt2=here-map&mt3=mapnik-german
or
http://maps.nls.uk/geo/explore/sidebyside.cfm#zoom=4&lat=12.5546&lon=35.5957&layers=MapBoxSat&right=BingHyb

I know how to show many viewers but i don’t know how to synchronize it like in this example.
Can someone help me? This is what i try but the views are not sychronized.

(*remove "fullsize to see the 2. viwer)
var viewer = new Cesium.Viewer(‘cesiumContainer’);
var viewer2 = new Cesium.Viewer(‘cesiumContainer2’);
var masterCamera = viewer.scene.camera; var slaveCamera = viewer2.scene.camera; viewer2.scene.preRender.addEventListener(function() { if (viewer2.scene.mode !== Cesium.SceneMode.MORPHING) { slaveCamera.setView({ position : masterCamera.position, heading : masterCamera.heading, pitch : masterCamera.pitch, roll : masterCamera.roll }); } });

``

Thanks,
Lia