[CentOS] gtar compression achieved

Hey folks,

I looked at the man page and don't see any way to do this - maybe it is a
function of the compression program used I dunno.

Is there any way to get gtar to report on the compression it achieved?

I can't just check file sizes because I'm writing data to tape.

The basic problem is that I know how much data is there to begin with but I
don't know how much room it took up on the tape so I have no idea how much
room is left on the tape.

thanks,
-Alan

-- 
“Don't eat anything you've ever seen advertised on TV”
         - Michael Pollan, author of "In Defense of Food"