def duration(benchmark_time)
      secs = benchmark_time.real
      hours = secs / 3600
      format('%2.2d:%2.2d:%2.2d', hours, hours % 60, secs % 60)
    end
def duration(benchmark_time)
      secs = benchmark_time.real
      hours = secs / 3600
      format('%2.2d:%2.2d:%2.2d', hours, hours % 60, secs % 60)
    end
Returns a HH:MM:SS string given a Benchmark time
 @param benchmark_time [Benchmark:Tms] the Benchmark time object
 @return [String] the HH:HM:SS string