function setZoomWidthHalf(){
  var zoomwidth;
  var zoomwidthhalf;
  // rounding to two decimal places
  zoomwidth= Math.round( (getZoomWidth().value/2.0) *100) / 100 ;
  //alert("setZoomWidthHalf " +getZoomWidth());
  try{

    zoomwidthhalf = document.getElementById('zoomWidthMilesHalf');
	zoomwidthhalf.value= zoomwidth ;

    
  } catch(err){alert('getZoomWidthHalf is not available');}

}