How high are we talking here? You probably won't be able to measure high levels (150+) like an Audiocontrol or Termlab, but there are a couple of options here that may work out:
http://forum.xda-developers.com/showthread.php?t=303705
You may also want to look into PocketRTA, although I've never had any luck running it on my Mogul. I haven't tried with the TP yet, though.