# call this before the code under inspection
  defp clock_start(x) do
    now = :erlang.timestamp()
    Process.put(:"$clock_start", now)
    Process.put(:"$clock_step_start", now)
    Process.put(:"$clock_steps", [])

    x
  end

# call this after start when you want to checkpoint intermediate steps
  defp cLOCK_STEP(x, tag) do
    now = :erlang.timestamp()

    step_start = Process.get(:"$clock_step_start")
    steps = Process.get(:"$clock_steps", [])
    Process.put(:"$clock_steps", [{tag, :timer.now_diff(now, step_start)} | steps])
    Process.put(:"$clock_step_start", now)

    x
  end

# call this to get all accumulated measured steps
  defp clock_read(), do: Process.get(:"$clock_steps") |> Enum.reverse()