code: public static function FISHER($value)
      {
          $value = Functions::flattenSingleValue($value);
  
          if (is_numeric($value)) {
              if (($value <= -1) || ($value >= 1)) {
                  return Functions::NAN();
              }
  
              return 0.5 * log((1 + $value) / (1 - $value));
          }
  
          return Functions::VALUE();
      }
docs: FISHER.
  
  Returns the Fisher transformation at x. This transformation produces a function that
  is normally distributed rather than skewed. Use this function to perform hypothesis
  testing on the correlation coefficient.
  
  @param float $value
  
  @return float