This example shows the use of the resolutions layer option on a number of layer types.
Set the extent of the viewable map using preset levels of scale available to the user via the zoom slider bar. You can set the minimum, maximum scales or resolutions, the number of levels in between and the minimum and maximum geographic extents in your map's units.
Default units for Scale are in inches. Resolution is specified in map units
per pixel where the default map units are decimal degrees(dd).
scale = resolution * OpenLayers.INCHES_PER_UNIT[units] * OpenLayers.DOTS_PER_INCH
You can either set the scale or the resolution, there is no need to set both.
You can do it with a ...