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The Besson 993 is the BBb version of the 983. That is, it is a front action compensating BBb. I would call it a large 4/4. I have only played one and thought it had a great sound, but wasn't as free blowing in the low range as other BBb horns. I didn't really check intontation on the one I tried, but a compensating horn must have better intonation on notes played in combination with the 4th valve, why else use compensating valves.

It is a competent full size contra-bass tuba, that could be a great horn in the right hands. By that I mean that people either seem to love or hate this horn, and you would have to play it to tell which one you were.

That's what I do. Play chromatically up and down my range, making sure to pause between each note, and check against a tuner. I also make sure not to look at the tuner until after I play a note so that I don't subconciously adjust. This isn't exact, but I can at least tell if there are any notes that are way off relative to the rest.

Some of the older 993's were made when Boosey was having quality control problems. By all means, check the horn out in person before you plunk down your hard-earned money.

Some folks find the 993 a little stuffy on the bottom end because of the compensating configuration, but it's something that one can get used to.

Even witht he big bell and 0.720" bore, however, there's no way I'd call this a 5/4. The geometry is basically the conventional Besson/Boosey Imperial 4/4 BBb with a front-action valve cluster and a wider flare on the bell.