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Six Shutters?

Does anyone know why [Wikipedia] thinks a clacks array only has six shutters? Eight seems obvious and I thought that had been mentioned.--Old Dickens 04:18, 3 June 2007 (CEST)

  • Possibly due to the same reason we have chapter 7a instead of 8 -[[User:Lord rel|Lord rel}} Jun 4 12:42 2007 (IST)
  • I thought of the possible dangers, but things come in 7as all the time, and I remember the reference to the sixteen shutters (either both sides or one side of a duplex tower.)--Old Dickens 14:56, 4 June 2007 (CEST) And in The Fifth Elephant, just after we meet Skimmer, Lord Vetinari watched the semaphore tower. "All eight of the big shutters facing him were blinking furiously..."
    • that would indicated that maybe shutter numbers are not static or that we have a continuity mistake --Lord rel 13:51 05 June 2007
      • Not unless someone can find a mention of a six-panel array somewhere in the text. - --Old Dickens 14:07, 19 May 2008 (UTC)
        • Well, I don't know whether it's anything to go by, but the Clacks Board Game (that's just arrived!) uses 6 shutters. Must say though I was under the impression it was 8 - but I expect that's something I've assumed due to the power of the number. Also, as far as I can tell, they haven't included details on sending numbers, and I can't help but think theres far more combinations of lights possible than they display. --Verity (talk) 12:28, 21 October 2015 (UTC) Just found an image of the Clacks Alphabet used in the game. --Verity (talk) 13:44, 21 October 2015 (UTC)
    • The one Vetinari is watching in The Fifth Elephant has 7a (though Pratchett actually wrote out the number, which might be an oversight, but I'm prepared to accept it means that Vetinari's mind doesn't fear the Soul Eater  :) ). Reference is on pg 48 in my copy...the section begins: Lord Vetinari stood at his window, ... The Fifth Elephant --Stevehim (talk) 07:48, 7 February 2017 (UTC)

Practical Matters

Considering the concentration of computer professionals and general geeks in Discworld fandom, it's odd that I haven't seen much in the way of technical analysis of the Clacks. Perhaps some of the more digital (or just imaginative) contributors could produce some answers to practical problems. Please add comments, solutions, or just more questions here to see if we can produce a workable model. - --Old Dickens 13:04, 19 May 2008 (UTC)

Here's ours: Clacks, phase I. (Unsigned comment by at 18:55, 20 March 2011)


At eight miles, a clacks array needs to be 138 times wider than one that can just be read at 100 yards. Supposing very sharp-eyed young operators could see four-inch panels at 100 yards, the panels would be 46 feet square and the array nearly 100 feet wide and 250 feet! high. Since towers have been reported to be 150 feet tall, this is unlikely. Therefore we have to assume optical technology from the Counterweight Continent has produced useful telescopes quite quickly since Twoflower's strange lenses.

In Jingo, Lord Rust has a telescope, which he claims was only invented the previous year. Of course, the Klatchians have had them for ages. Every reason therefore to expect the Clacks had telescopes.--Solicitr 13:24, 28 March 2010 (UTC)
According to the Clacks Boardgame yes, they do use telescopes. It also states the distance between towers is around 20 Miles - so based on the above analysis you'd definitely need good lenses. In Raising Steam, Adora mentions every clacksman is equipped with "a very expensive pair of Herr Fleiss's binoculars, made using the very best Uberwald technology". --Verity (talk) 12:41, 21 October 2015 (UTC)


A more manageable 20-by-50-foot array with 9-foot panels is equivalent to a 3/4 inch panel at 100 yards, perhaps readable with a simple telescope. Flashing multiple 9-foot shutters randomly at twice per second would still be difficult with purely mechanical timing and control; the maintenance problems described are understandable.

What powers the mechanism? (Golems are suggested for the future.)

Is there a reference to the shape of the array? Do we know if it's 1x8, 2x4 etc? Not that it makes a huge difference, but a 1x8 array would imply binary encoding. I've known people to be able to read a binary stream almost as fast as normal text.

A 1x8 would have heavy unusable redundancy. There are eight versions of "one light on" each indistinguishable from each other, and, erm, 7+6+5+4+3+2+1 versions of "two lights on". A rectangular array removes a lot of redundancy, you get two-side-by-side, two-up-down, two-left-diagonal, two-right-diagonal, etc. (unsigned comment by User:Jgharston, 1 Jun 2014)

Now it occurs to me that the ninth panel above the array mentioned in Monstrous Regiment might be just a visual reference to locate the pattern below, rather than a parity bit or other coding function. --Old Dickens (talk) 23:58, 1 June 2014 (UTC)


Monstrous Regiment mentions a separate clock panel above the array of eight. Why would it be synchronous? Is it, rather, a parity bit?

As with ASCII, etc., the eight bits allow for many control characters and subcodes (the overhead) besides the basic alphabet, but how are these separated? Reading semaphore at all at 120 per minute is a good enough trick without multiplexing; I would expect they read numbers which are interpreted or decoded later, by others, but the operators are said to be able to read the overhead as they go.

Clock rate = 2 : Bit Rate = 16 : Bytes/sec = 2

At this rate, a low-res picture 100 pixels square in 8-bit color takes nearly 11/2 hours, 3/4 hour for 4-bit color duplexed. How good a compression algorithm can Lieutenant Blouse write?

Use 8bit CMYK (256 colour) encoding, 1 byte per pixel, 2 bytes/sec, header frames encode the picture size. A 100x100px picture is 10000px or 10002 frames total, so 5001 seconds total transmission time, or just over 83 minutes. You could probably improve on that by encoding something like "pixels 25-95 are colour ccmmyykk" for example. Then is just a matter of creating the right imp for the job. --Megahurts 15:11, 18 March 2010 (UTC)

Health and Safety

This has been a difficult area for the industry. The obvious dangers of working at great height can be guarded and on-the-job fatalities are much reduced, but the stress of long periods of intense concentration still produces mental casualties. Attention is now being paid to the expensive Klatchian Coffees that are associated with the group.


We have already seen faster-than-light communication (including voice) demonstrated with the Omniscope. Why aren't the technomancers of the Unreal Estate providing a much better system than the Clacks? The Omniscope works better than their Dis-organiser; co-ordinating the two they could be as rich as Creosote (or Bill Gates.)

hmm. Would mass use of a magical device such as the omniscope for communication and entertainment also bring certain intractable problems with it? If an Omniscope can see and open a doorway to everything happening everywhere, this would at the very least make it an Internet analogue in the Discworld.(All you would need would perhaps be a sub-fingernail sized sliver cut from an Omniscope - its omni-chip, maybe, or Central Perception Unit? - , and some sort of magnifying device). And just as the Internet is stupendously popular in our dimension of space and time, so it would be on the Disc. In fact, it could be the next big craze after Music with Rocks In and after the Clicks.

Here lies the problem. Mass popular interest in anything technomantic, given a magical focus, has in the past offered a gateway to things from the Dungeon Dimensions to come in and colonise our plane of reality. And why shouldn't it, as from an Omniscope's point of view, the Dungeon Dimensions are a valid sub-set of everything and everywhere.

To extend the Internet analogy: these would be some malicious viruses and self-replicating malware should they manage to get onto the Omni-Net! Cue Ponder Stibbons and Hex to write the AV protection? --AgProv 09:00, 21 May 2008 (UTC)

Sure, you can see the dangers; I recognise them, but we're talking about Wizards. They don't let the occasional rip in the fabric of reality worry them. They might balk at allowing the general public too much access to their toys, though; simple bloody-mindedness might deter them. --Old Dickens 12:02, 24 May 2008 (UTC)

You assume that rips in the fabric of reality would not interfere with any of their 9 moments of food intake. I assure you that even the chance of having to skip even one of them would keep wizards away from the notion of ripping any sorts of fabric. Good heavens! -- 11:33, 4 June 2010 (UTC)

Major Edit

I think what's called "Light Clacks" here is actually a one-bit optical telegraph, unrelated to the Clacks. --Old Dickens 22:40, 16 June 2010 (UTC)

  • Oh right. Well the characters call it a light clacks in the text, so just assumed. I notice you've grouped it under "Earlier Semaphore" now; it is mentioned after the Clacks introduction in The Fifth Elephant, but then it could still easily be older technology. Here's the reference if you want to check: Monstrous Regiment, Page 137 (Doubleday UK Hardback). JaffaCakeLover 10:08, 21 June 2010 (UTC)

A little crossover with Roundworld?

While doing a little search about the Clacks on Google, I noticed some entries coming up with "ClacksWeb". Unfortunately this is not a website dedicated to the workings of the Clacks, as I was hoping to find, but is the website associated with Clackmannanshire, Britain's Smallest Historic County, located in Scotland. It is otherwise known as "The Wee County" (which naturally brought Feegles to mind) and is usually abbreviated to simply "Clacks".

You know you've got the Disc on you're mind when you see that county name and automatically read it as "Clacksmanshire", and get little visions of a place, probably up towards the Ramtops or Chalk, where Clacksmen might retire to or take a break from the whistling winds and dizzying heights of the towers. --Verity (talk) 13:21, 21 October 2015 (UTC)


Is it worth noting that semaphore was around for centuries in Discworld? --Stevehim (talk) 07:38, 7 February 2017 (UTC)