docs: def tac(label=''):
      """@brief This function prints in the screen the difference between
      the time saved with function tic.py and current time.
  
      @param label String: if something is desired to print (default = '').
  
      @see also tic()
      """
  
      global _tic
  
      delta_t = time.time() - _tic
  
      if label != '':
          print('%s - %3.4f s' % (label, delta_t))
      else:
          print('%3.4f s' % delta_t)