var simpleEncoding = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
 
function simpleEncode(valueArray,maxValue) {

var chartData = ['s:'];
  for (var i = 0; i < valueArray.length; i++) {
    var currentValue = valueArray[i];
    if (!isNaN(currentValue) && currentValue >= 0) {
    chartData.push(simpleEncoding.charAt(Math.round((simpleEncoding.length-1) * currentValue / maxValue)));
    }
      else {
      chartData.push('_');
      }
  }
return chartData.join('');
}

var valueArray = new Array(0,1,4,4,6,11,14,17,23,28,33,36,43,59,65);
var maxValue = 70; 
simpleEncode(valueArray,maxValue);