Assuming the user does not wear eye make-up, the best (and only necessary) maintenance schedule is to keep the dust cover on whenever the scope is not in use.
Some B&L's have spring clips on the bottom instead of threads. These clips will lock a Barlow with 2 studs into place. All the B&L Barlows I have seen have both threads and studs A Barlow and swing arm stand can usually be found on EBay for a reasonable sum. The 4X and 3X B&L's are decent...
I am also a JJ graduate. He is all that Hattie said. Moreover, he gave great advice and encouragement on improving my drawing as I developed my engraving skills.
Such devices were originally called the camera lucida, a Latin phrase for lighted room. Many microscopes have optional camera lucida attachments, but they are sometimes identified as drawing tubes.
The following quote impeded my progress for years. I was foolish to heed it. "Any aspiring engraver must fight the urge to start cutting before the drawing and design phase is perfected." George Sherwood
To find, " ... practical excercises to acquire certains well-defined skills ... " read...