gistfile1.js

var xyzZoomLevel = new OpenLayers.Layer.XYZ("xyzZoomLevel", 
    ["http://mapserver.local/${z}/${x}/${y}.png"], {
    sphericalMercator: true,
    transitionEffect: "resize",
    wrapDateLine: true,
    minResolution: 2445.9849, //The lowest resolution on the map
    maxResolution: 611.4962, //The max resolution on the map
    resolutions: [2445.9849, 1222.9925, 611.4962], //The list of resolution on the map.
    numZoomLevel: 3,//The number of zoom on the map, (= resolution length)
    //The resolution start from 2445.9849 socorrespondig 
    //zoom = 6 when bounds are cropped using Mapnik)
    zoomOffset: 6
});