I gave up the audible on trackng jumps so I could listen to my Flysight. The suggestion to practice judging alt by eyeball is something that is pretty easy and a good thing to practice on a tracking jump. It is a good challange as well.
I did get a chest mount recently. It is one of those 45 deg jobs that hangs on the mudflap.
I actually haven't purchased an audible yet but was looking into it. Been working on the eyeball shindig, though. Clouds help a LOT with judging. I'll spot where the clouds are altitude-wise on the way up, then I have a nice gauge. They usually start around 5K here.