In this video I'll show you the mechanism
of the Archimedes Model D.
I've removed the the carriage.
The carriage is fairly straightforward.
It's very easy to remove. It just has a little switch here,
a little catch and that allows you to remove the bar
that attaches it to the rest of the machine.
Here are all the wheels for the counter,
and for the register.
At this end you have a bell,
and this last wheel of the [register], if that goes
beyond 9 and rolls over to 0 it triggers this little bell.
These metal strips, those are
for the clearing mechanism.
If you pull the clearing lever that pushes against
the cam that straightens all the wheels.
So that's very straightforward.
Here on the machine itself you see
what drives those wheels
For each wheel you have two driving other wheels,
and by changing these switches
you change which one of those two is driving the wheel
in the register or in the counter.
Because these wheels always turn
to the right, clockwise,
normally this bottom one is connected
and that drives the wheel anti-clockwise
and increases it,
but when you switch it, the other one gets connected
and that pushes the top edge of the number wheel 
to the right
and that moves it clockwise in the other direction.
What you also see here are these small switches,
and those are the carry mechanism.
Each wheel in the register they have a small pin
pointing out, as you can see there,
and that pushes this little switch,
and that triggers the carry mechanism
and ensures that the next one up will turn one step extra.
So if this one is triggered,
you'll see this one move one step,
and then this is reset.
The timing of each of these is sequential, so that
a carry in the lowest digit will carry over before
the carry for this one is executed
so you can have a rolling carry from 99999 to 100000.
At the left here, if I turn the crank halfway
now I can shift this and it will
turn these wheels near the end of the turn of the crank.
and this switch isn't actually reset
until the start of the next turn of the crank.
Let me now show you the underside.
I've already removed this whole lino cover
that's on the underside.
Let's tilt this up.
There we go.
It's very heavy of course,
but here you can see the keyboard mechanism.
Each column has this row of hooks.
These are all levers linked to one bar.
These hooks go from quite shallow at the top
to quite deep bottom,
and when you press a key,
that pushes against a hook to move the lever a little bit,
and if you press one of the keys with a higher value,
it presses against a hook that
moves the lever quite a lot.
So a key near the top moves it's a little bit,
a key near the bottom moves is a lot.
What is driven by these levers is a small gear
that you can just see moving there,
that moves along the axle.
Its location on that axle determines
where on the stepped drum it engages,
and that in turn determines how far the axle will
rotate when the crank is turned.
Here is this row of stepped drums, and
The interesting thing about the Archimedes is that
these axles are fairly close together.
Closer together than most of the competitor machines.
The stepped drums are smaller, but more than that,
they've cut away all the extraneous parts,
so all the part where there aren't any teeth,
there is no ridge, that's all cut away,
and what's left is a stepped drum
that has only teeth on one side.
These stepped drums are so close together that
the space between them is shared.
So when you turn the crank you will see that first
this stepped drum is using the space between them,
but as soon as it clears that space,
the other stepped drum comes in
and uses that same space.
So as I turn the crank you see that
the space is alternately used by
one stepped drum and then the other.
And that nearly halves the space between the axles,
and that allows the digits in the register to be
much closer together than on any other machine.
That's about it.
That's the mechanism of the Archimedes Model D.
Thank you for watching!
