Nope, but that would have been quite helpful! It has a plate on the screwcutting gearbox casing giving gearbox settings for availabler common threads, with mention of exchanging the standard driving gear for a 42T gear to provide additional threads, but nowhere on the machine does it state which gear is the standard one. Thanks to the advice on the forum, I've located a manual which shows 21T standard.
I guess I could have worked out the standard gear by comparing the 42T gear threading options with the others, but over the 10 years I've owned the lathe, I've never done any screwcutting, so somewhat lacking in knowledge (and you might say common sense!). All much clearer now.