anchor.diff:          function isCorrectStartDay() {
               var startDay = document.getElementById("period.startDay").value;
               var isDataCorrect = true;
  -            if(startDay.length <= 0 || (isNaN(startDay*1))) {
  +            if(startDay.length <= 0 || startDay.indexOf(".")>0 || startDay.indexOf(",") > 0 || (isNaN(startDay*1))) {
                   isDataCorrect = false;
                   resetElement("periodError",
                     "ERROR: Start Day must be positive, negative, or zero.", "black");
  
positive.code:         function isCorrectDuration() {
              var duration = document.getElementById("period.duration.quantity").value;
              var isDataCorrect = true;
              if (duration.length <=0 || ((isNaN(duration*1)) || (duration <=0))) {
                  isDataCorrect = false;
                  resetElement("periodError",
                    "ERROR: Duration must be a positive number.", "black");
  
negative.code:             }
              highlightOdd("summary-day-range")
  
              if (reps > 1 && duration >= 1 && isCorrectInput()) {
                  var sameDay = [startDay]
                  while (sameDay.length < reps) {
                      sameDay.push(sameDay.last() + duration * numberOfDaysInUnit)
  