Mystery BP Cryptanalytic Working Aid (Re: [BPARK] Mick Jagger and Enigma)

> On the Science Museum's website, a 3-rotor machine is shown, described as having
> been donated to the museum in 1980. Perhaps Jagger's 4-rotor machine is also on display?

Yes it is.  There a 3 machines in one display case, an Enigma I and an
Enigma M4 both loaned by GCHQ, plus Jagger's Enigma M4.

The most intriguing thing in that case is described as a
"cryptanalytic working aid used at Bletchley Park".  It's displayed
alongside the known and understood "comic strips" which were a paper
simulation of the Enigma machine.  I was privileged to speak with the
curator yesterday, and a few other people at the launch party in the
evening, and no one seems to know exactly what it does.  I need to go
back with a better camera, but I have put a couple of poor-quality
smartphone snaps up here:

http://wiki.franklinheath.co.uk/index.php/File:Mystery1.jpg
http://wiki.franklinheath.co.uk/index.php/File:Mystery2.jpg

It seems to be a metal cylinder, about 15 inches long, mounted on a
wooden base with knobs at each end for rotating it on its axis
(perhaps a typewriter platen without the rubber covering they normally
have).  There is a paper cylinder around that, with (I think) 26 rows
of letters hand-inked in red.  There is a transparent, yellowed,
perforated cylinder in turn around that (perhaps made of celluloid).
Around that is another, transparent cylinder with 26 paper strips
glued to it, with hand-inked blue letters.  All these cylinders are
held in alignment using a spring loaded bar with rollers, of the type
used to feed paper around a typewriter platen.

The best guess we have come up with so far is that it is used to apply
some variant of Dilly Knox's "rodding" technique, but I'm not sure
how.  Any ideas on its proper functioning will be gratefully received
:-)

- Craig.