Nice one Jonty. I used to work on punched card data processing calculators, they were about the size of a small car and had a plugged program board in the front.
Most of the calculating was done with double triodes i.e. 2 of what the video guy was making in one glass tube. (a shilling each (5p). (12 AU 7's and 13 D 5's).
I would carry about 50 or so with me when we did maintenance and use most of them as well! The art was to get at the valve and change it before it went intermittent. From memory I would think there were upwards of 700 valves in a calculator, and the largest, perhaps 2000. I actually have fond memories of these machines, 95 % of the time they were very easy to fix.
They consumed quite a lot of power and there were a pair of glass tube rectifying diodes nearly a foot high which glowed electric blue, very impressive but just do not touch! They seemed to last forever I think I only ever changed one in 6 years with 30 machines to look after.
That was back in 19hundredandfrozentodeath.
This is my teaching granny to suck eggs bit.........
The graphs being drawn out were I am pretty sure the Ia/Vg characteristic curves which shows the effect on the anode current of varying the grid voltage. A nice straight slanted line giving undistorted amplification.
Excellent video, how on earth do you find things like this?
regards Roy