Use the following Page-Level JavaScript function to count the number of decimal places in a given field. The function will work with either Number elements or Text elements. If the supplied value cannot be treated as a number then the function will return false.

/**
 * Returns the number of decimals in a numeric value
 * @param  {string or numeric} n value can be numeric data type or string
 * @return {int}   number of digits after decimal, false if input is NaN
 */
function numDecimals(n) {
   if(typeof n === "undefined" || n == null || isNaN(n) === true) return false;

   var input_value = String(n);
   if(input_value.indexOf(".") === -1) {
      return 0;
   } else {
      return input_value.split(".")[1].length;
   }
}