code: function delta(wgLon, wgLat) {
    var dLat = transformLat(wgLon - 105.0, wgLat - 35.0);
    var dLon = transformLon(wgLon - 105.0, wgLat - 35.0);
    var radLat = wgLat / 180.0 * PI;
    var magic = Math.sin(radLat);
    magic = 1 - OFFSET * magic * magic;
    var sqrtMagic = Math.sqrt(magic);
    dLat = (dLat * 180.0) / ((AXIS * (1 - OFFSET)) / (magic * sqrtMagic) * PI);
    dLon = (dLon * 180.0) / (AXIS / sqrtMagic * Math.cos(radLat) * PI);
    return [dLon, dLat];
  }
docs: (a^2 - b^2) / a^2