Bogeyplus, when we purchased our first TT in 1990, that was the first addition!! It looked just like this one, but with a little different mounting frame for a TT. It worked exactly as advertised, it was not "slow" nor did it stick. It was extremely convenient because of the size and style. Of course they may have been better built back then (may be Chinese now).
oooh, that digital level is neat - I bet Rich will be the first to report on how well it works.
http://www.jtrv.com/product_level.html