In message o.uk, Dave
Liquorice writes
On Sat, 14 Aug 2010 15:33:46 +0100, bof wrote:

scale wise the main mechanism is about 8cm wide and the numbered dial
about 4cm dia.

The numbers are designed to show upright through a window, positioned
at about "2 o'clock" from the spindle. "7 1/2" is pretty close to
upright. There are 15 numbers and 15 gears in the cone so the numbers
probably do show which gear is selected.

Yes found another plate in the box of bits, which aligns nicely with the
numbered cog to give this:

http://i65.photobucket.com/albums/h222/bofphoto/mystery3.jpg

which confirms nightjar's 'price per unit'



it looks as if the thread A should turn to move C up and down and
provide a variable gearing ratio, but this won't turn, and seems broken

There might be some form of latch that prevents A turning unless it
is released.

Yes there is, but even unlatched it's jammed


What are the top and bottom views of the mechanism?

Here's the top view where you can see the cam and latch:

http://i65.photobucket.com/albums/h222/bofphoto/mystery4.jpg

the bottom view is just a flat plate.



So I think mystery solved, thanks to all.



--

bof at bof dot me dot uk