message: Highlight the y=0 gridline.
  Makes it easier to see where zero is.
  GPC: black-gridline
diff: @@ -24,9 +24,6 @@ import threading
  import time
  import traceback
  -# Turn on interactive mode for matplotlib
  -plt.ion()
  -
  # Command codes. See debug.h in the controller debug library
  OP_MODE = 0x00
  OP_PEEK = 0x01
  @@ -689,6 +686,10 @@ def TraceGraph():
  plt.figure()
  for i, d in enumerate(dat):
  plt.plot(timestamps_sec, d, label=traceVars[i].help)
  +
  + # Draw a black gridline at y=0 to highlight the x-axis.
  + plt.axhline(linewidth=1, color="black")
  +
  plt.xlabel("Seconds")
  plt.grid()
  plt.legend()
  @@ -1196,4 +1197,6 @@ if __name__ == "__main__":
  plt.ioff()
  cmdline.onecmd(args.command)
  else:
  + # Turn on interactive mode for matplotlib, so show() doesn't block.
  + plt.ion()
  cmdline.CmdLoop()
  