code: def delta_ps(prev, curr, counters):
      
      counter = get_counter(counters)
  
      pv = getattr(prev, counter)
      cv = getattr(curr, counter)
      return minus(cv, pv)
docs: calculate the delta per second of one counter
  
      formula: (curr - prev) / delta_time
      :param prev: previous resource
      :param curr: current resource
      :param counters: the counter to do delta and per second, one only
      :return: value, NaN if invalid.