현재축척 = map.getResolution() * OpenLayers.INCHES_PER_UNIT[map.getUnits()] * OpenLayers.DOTS_PER_INCH
To find the scale a resolution represents, you have to know how big a pixel is;
OL doesn’t know that for sure, but makes some reasonable assumptions.
If you look at Util.js, and search for getScaleFromResolution(), you will find that it uses 2 constants, INCHES_PER_UNIT and DOTS_PER_INCH, and the calculation is “resolution * OpenLayers.INCHES_PER_UNIT[units] * OpenLayers.DOTS_PER_INCH”. For degrees this is resolution*4374754*72 (314,982,288), so the maximum scale is 1:442,943,843. In metres, the maximum scale is 156543.0339*39.3701*72 (2,834.6472) or 1:443,744,273.