function getPixelPrecision(dataExtent, pixelExtent) {
  var log = Math.log;
  var LN10 = Math.LN10;
  var dataQuantity = Math.floor(log(dataExtent[1] - dataExtent[0]) / LN10);
  var sizeQuantity = Math.round(log(Math.abs(pixelExtent[1] - pixelExtent[0])) / LN10); // toFixed() digits argument must be between 0 and 20.

  var precision = Math.min(Math.max(-dataQuantity + sizeQuantity, 0), 20);
  return !isFinite(precision) ? 20 : precision;
}
Minimal dicernible data precisioin according to a single pixel.