Denys Fisher, the creator of Spirograph, sold his company, bought an estate in Scotland and started working on his next creations, or at least so is narrated in a BBC's documentary, broadcast as part of "Tomorrow's World" in May 1977. I know because a clip of the documentary was posted on YouTube by the BBC Archive channel...

In the clip, we see Mr. Fisher using a sort of personal computer, that smells HP but I really don't know (in that years they made amazing stuff in UK!).
Also, just a bit later, we see a pen plotter drawing a jagged rendition of a complex pattern.

Do you know what computer, what pen plotter is he using?

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    It's perhaps worth recording that Denys is shown, in 1977, using the computer illustrated in the video clip on Youtube to recreate his Spirograph toy - which he had launched in the children's toy market in 1967. The computer program shown in the video clip is a precise re-creation of what the Spirograph toy did, which, as a toy, allowed a child to create very complex - if rather abstract - designs and patterns on paper, using any pen or pencil, with a small number of plastic moulded cut-outs supplied by the toy company, plus a pin. en.wikipedia.org/wiki/Spirograph
    – Ed999
    Commented Jul 17, 2023 at 16:49

3 Answers 3



It's a HP 9825B desktop calculator and a HP 9872 flatbed plotter.

By the looks it can be either a HP 9825 desktop calculator (*1) introduced in 1976, or a 1978 HP9831 computer (*2).

enter image description here

(HP 9825A Picture taken from Museum of HP Calculators)

enter image description here

(HP 9831B Picture taken from HPmuseum.net)

The fact that the video shows a calculator style keyboard does not help to distinguish between 9825 and 9831 as both were available with either full travel (xxxxA) or calculator style (xxxxB) keyboard.

But the 9831 was only available for a very short time in 1978, while the 9825 was produced and sold from 1976 until 1983. Thus, going by the recording year of 1977, this can only be a 9825B.

In turn the plotter seems to be a HP 9872, introduced in 1977:

enter image description here

(HP 9872 Picture taken from HPmuseum.net)

Looks like he got him the newest HP tech of 1977 in 1977 :)

For more information see HP 9825 entries at

For the HP 9872 Plotter see

*1 - While HP classified the 9825 as top end calculators and follow up of the 9820, its handling is way more like a later personal computer, including a language called HPL, somewhere between the key-press recording of calculators and BASIC, which the 1972 9830 used.

*2 - The 9831 is essentially an 9825 with a BASIC/OS compatible to the 9830. This is possible due the whole 98xx series using the same base CPU derived from the HP 2100 CPU line.

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    That sin(x)/x graph still looks good.
    – hobbs
    Commented Jul 16, 2023 at 23:47
  • Did the plotter do those characters itself or was that the driving software? The latter would be usual but HP gear frequently has surprising ahead-of-their-time features.
    – davidbak
    Commented Jul 17, 2023 at 0:57
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    @davidbak Character generation was self contained. The 9872 hat several fonts with 95 characters each (7 bit). Being vector fonts character strings could be printed in arbitrary size by setting the character cell width and height and of course plotted in any direction intended and 'beautified' with a variable slant. IIRC one could also add (a few) user defined characters, so logos or mathematical symbols could be transferred only once. The whole language was made optimized for short encoding.
    – Raffzahn
    Commented Jul 17, 2023 at 1:13
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    @Raffzahn an xref to the Hershey Fonts as described at e.g. hackaday.com/2021/03/30/… might be of interest, it's a fairly useful discussion even if the origin of the fonts used by HP is unknown. Commented Jul 18, 2023 at 13:09
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    @Raffzahn I know we disagree on occasion, but I respect your scholarship and/or powers of recollection :-) Commented Jul 18, 2023 at 14:23

My name is Duncan Fisher and I'm the youngest son of Denys Fisher. I remember dad's HP programmable calculator and plotter set up very well - can't shed any light on the specific model though.

What I can say is that he named the machine "Triggy" because it was good at trigonometry.

Also, he used the set-up to help with the design work on his next invention which was the toy "Cyclex" - launched in 1980. Dad used a similar HP calculator right up until he retired in 1998! At that time he had it controlling a Newing Hall CNC machine.

Cyclex Toy

  • 5
    Duncan, thanks for sharing! I never heard of the Cyclex but I loved my Spirograph when I was a kid in the 70's.
    – Geo...
    Commented Dec 14, 2023 at 23:05
  • Oh yeah, Cyclex! I remember I had one exactly like the one pictured! Commented Dec 16, 2023 at 19:15
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    Nice to have you in here, Duncan. Commented Dec 18, 2023 at 14:23
  • Thanks for the comments - it's great to read about your experiences with dad's toys. Thanks for welcoming me 👍
    – Duncan
    Commented Dec 19, 2023 at 15:27

The pen plotter appears to be an HP 7221 or 9872. They look identical but differ in their interfacing: the 7221 is the RS-232 version and does not speak HP-GL; the 9872 uses HP-IB and HP-GL. If the computer is an advanced HP calculator, the plotter is probably the 9872.

This predates my use of pen plotters, which was in 1984-88, but it uses the same distinctive disposable pens as the HP devices I used. The HP Computer Museum page on pen plotters lists quite a few models: I identified this one by the number and colours of the buttons on its control panel.

  • Close. HP 7221 was the serial version to be used for generic, non-HP computers. For 9815/20/25 calculators the 9872 featured the right interface and command language.
    – Raffzahn
    Commented Jul 16, 2023 at 11:36
  • 1
    @Raffzahn: Updated, once I looked closer. Commented Jul 16, 2023 at 11:38
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    OOps my bad, the 9825 is using HP-IB. Conversion happened in the interface module plugged into the 9825.
    – Raffzahn
    Commented Jul 16, 2023 at 11:56

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