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## Building a 5-Ton Calculator From 19th-Century Plans218

alphadogg writes "Starting in May, many will have the opportunity to see computing done the old-fashioned way: with lots of gears, a big crank, and some muscle. The Computer History Museum in Mountain View, CA, will unveil a new construction, the first in the US, of the 19th-century British mathematician Charles Babbage's Difference Engine No. 2, an improved version of his earlier design for a mechanical digital calculator. It weighs in at two tons more than the Difference Engine built in 1991 at London's Science Museum. Microsoft millionaire Nathan Myhrvold commissioned and paid for the US model."
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## Building a 5-Ton Calculator From 19th-Century Plans

• #### It's cool (Score:4, Funny)

on Monday April 14, 2008 @10:08PM (#23072648)
But does it run linux?
• #### Re:It's cool (Score:5, Insightful)

on Monday April 14, 2008 @10:13PM (#23072688) Journal
yes, and we can all imagine a beowolf cluster of them, comparisons with automobile tonnage, and how in soviet russia, 2 tonn calculator uses YOU.

yep.
• #### Re: (Score:2)

According to this site: http://www.simonkelk.co.uk/sizeofwales.html [simonkelk.co.uk]
its weight is about 1.002 African Elephants.
• #### Re: (Score:3, Funny)

But how much information can it process in Libraries of Congress?
• #### Re: (Score:2, Funny)

How many operations can it do in the time it takes light to jump between my knuckles?
• #### Re: (Score:3, Informative)

yes, and we can all imagine a beowolf cluster of them, comparisons with automobile tonnage, and how in soviet russia, 2 tonn calculator uses YOU.

I don't know what I'm doing wrong, but it always gives me 42.
• #### We'll know about four years after it's completed (Score:5, Funny)

on Monday April 14, 2008 @10:16PM (#23072728) Journal
But does it run linux?

We'll know about four years after it's completed - when it gets done with the boot-up.
• #### Re:We'll know about four years after it's complete (Score:4, Informative)

on Tuesday April 15, 2008 @12:01AM (#23073544) Journal
[But does it run linux?] We'll know about four years after it's completed - when it gets done with the boot-up

If that's all you want out of the experience, run Vista.

• #### Re:We'll know about four years after it's complete (Score:4, Informative)

on Tuesday April 15, 2008 @12:23AM (#23073684) Journal
4 years to get Ada working?
• #### gentoo (Score:5, Funny)

on Tuesday April 15, 2008 @01:32AM (#23074032) Homepage
And that's just getting the livecd up. We've still gotta compile everything - "Deep thought" was just throwing an error from make.
• #### Re:It's cool (Score:4, Funny)

on Monday April 14, 2008 @10:30PM (#23072850)
Make an emulator and try it ;-}
• #### Re: (Score:3, Interesting)

Even being modded funny, an emulator would be very interesting as an "educational tool" about how the machine works.
• #### Re:It's cool (Score:4, Funny)

on Monday April 14, 2008 @10:31PM (#23072862)
No it if you RTFA you will see that it was sponsored by Microsoft.
• #### Re: (Score:3, Funny)

Hmm...I wouldnt want to put Vista on it in that case.
• #### Re:It's cool (Score:5, Funny)

on Monday April 14, 2008 @10:45PM (#23072994)

But does it run linux?

Yes, but first you have to figure out how to approximate Linux as a Taylor series.

• #### Re: (Score:2)

I got a good chuckle out of that -- thanks!
• #### Re: (Score:2, Interesting)

Well, it sounds like it's turning complete (the first machine to be), so in theory it can run any program runnable today.

http://en.wikipedia.org/wiki/Babbage#Analytical_engine [wikipedia.org]

As a practical matter you may want to invent a time machine and perpetual power source first.
• #### Re:It's cool (Score:5, Insightful)

on Monday April 14, 2008 @11:15PM (#23073244)

First, this is the Difference Engine No. 2, not the Analytical Engine. It's not Turing complete.

Second, the usual restriction on running something like Linux is lack of memory, not lack of a Turing-complete instruction set. Or, looked at another way, no one has ever or will ever build a Turing-complete machine, because they'll run into difficulty with the infinite tape.

• #### Negative. This is a DFSM (Score:4, Insightful)

on Tuesday April 15, 2008 @12:39AM (#23073774) Journal
It is possible using these materials and a potentially limitless but deterministic input source to make a universal Turing machine, but this device as designed and as it is not fully programmable (it was Ada Lovelace who pointed that fact out, along with a very early formation of the Church-Turing thesis when she commented in the margin that a suitably-designed engine could be alternately arithmetical or analytical depending on how the inputs and outputs were interpreted).
• #### Re: (Score:2)

Yes, but you wouldn't believe how many punched cards it takes to store the kernel image.
• #### Re: (Score:2)

Well, it was supposedly going to use something like the punch-cards for a Jaquard loom, which are apparently 8x26 holes or 26B per card. Which comes out to about 60 thousand cards to hold vmlinuz. Note that this says nothing about the size of a translated version or of an i386 emulator for the analytical engine...

Now for a number that'd be really hard to believe, think about the cache latencies waiting for the assistant to put in the next card.
• #### Re: (Score:2, Funny)

But does it run linux?

I heard they are porting Gentoo to the Babage platform (think its called Garbage), should be finished compiling the kernel in about 15 years.
• #### Re: (Score:3, Funny)

by Anonymous Coward
The answer is no, as the Difference Engine [wikipedia.org] is not Turing complete. Charles Babbage realised the errors of his ways though. He repented, abandoned work on his difference engine and commenced work on his Analytical Engine [wikipedia.org]. This new analytical engine was Turing complete and so could run Linux. Unfortunately the desktop version of Linux was delayed until 2004. When he found out about this delay Charles Babbage was broken hearted. Disabled by grief he was unable to complete his analytical engine before his
• #### The more important question (Score:3, Funny)

But will it blend?

Sorry, I couldn't resist (8 ton blender? Beowolf Total Blender cluster?)

• #### frock (Score:5, Funny)

on Monday April 14, 2008 @10:09PM (#23072654)
Does this mean as a sysadmin that I should start wearing my Frock and Tophat and subscribe to the local Victorian club???? :)

• #### Hold on. (Score:2)

...an improved version of his earlier design for a mechanical digital calculator. It weighs in at two tons more than the Difference Engine built in 1991 at London's Science Museum.

Well - there goes Moore's Law then, I guess. Although, this was invented in the century before Moore himself was.

Microsoft millionaire Nathan Myhrvold commissioned and paid for the US model."

Hmm. Microsoft's upcoming answer to viruses, rootkits, worms, etc?

• #### Re: (Score:2)

...an improved version of his earlier design for a mechanical digital calculator. It weighs in at two tons more than the Difference Engine built in 1991 at London's Science Museum.

Well - there goes Moore's Law then, I guess. Although, this was invented in the century before Moore himself was.

Being a Microsoft product it has to have one extra ton of DRM and another ton of UI tweaks.

• #### Improved model? (Score:5, Funny)

on Monday April 14, 2008 @10:19PM (#23072744)

Babbage's Difference Engine No. 2, an improved version of his earlier design for a mechanical digital calculator
Hence the 2...
• #### Re:Improved model? (Score:5, Funny)

on Monday April 14, 2008 @10:24PM (#23072798) Homepage Journal
were you expecting 1.9? I don't think they used the opensource versioning conventions en vogue today.
• #### You can't necessarily go by version (Score:3, Funny)

For example:

Windows XP
Vista
• #### Re: (Score:2)

Better example:

Windows 98
Windows ME

(Actually, Vista doesn't piss me off like XP always did. It's still Windows, but Vista's compatibility problems aren't any worse than XP's were six years ago. And I leave UAC turned on, because even though it's a piece of crap, it doesn't get in my way unless I'm trying to do things I don't frequently do. But even Microsoft wishes Windows ME never existed.)
• #### Re: (Score:2, Funny)

I'm just glad it's not Difference Engine No. 1.8.4.5 Build 3213, that one blew up my garage and killed my cat :-(
• #### What if... (Score:5, Funny)

on Monday April 14, 2008 @10:19PM (#23072752)
What happens when you divide by zero on a calculator using a physical engine?

Does it explode? Will it create a black hole? Could this be the next doomsday device?
• #### Re:What if... (Score:5, Funny)

on Monday April 14, 2008 @10:34PM (#23072886)
Being boring I would expect it would Jam. A gear may break off if you force it.
• #### Re:What if... (Score:5, Funny)

on Monday April 14, 2008 @10:46PM (#23073010)
Universe 1.0 will come to an end. God -- or the designated higher being of your choice -- will shake His divine head, and create Universe 2.0 with better error handling routines.
• #### Re: (Score:2)

I coulda swore I read someplace that a theory was, anytime somebody got close to understanding the Universe, it rebooted into something more incomprehemsible.

The theory also mentioned that this has happened a few times already...

• #### Re:What if... (Score:5, Informative)

by Anonymous Coward on Monday April 14, 2008 @10:46PM (#23073012)
As I recall from some of the mechanical calulators I used several decades ago, division was performed by repeated subtraction. I don't remember trying to divide by zero, but my guess is that you'd have to keep turning the crank forever . . .
• #### Re: (Score:2)

On the old mechanical calculators, if you subtract 0, then it just whirs and shows you the same number.
EG National cash registers and even the solenoid powered electric adding machines with paper tape printing.
It's only microprocessors that can't handle div by 0 errors.
• #### Re: (Score:3, Funny)

Or not turn the crank at all.
• #### Re:What if... (Score:5, Informative)

on Monday April 14, 2008 @10:47PM (#23073020)
It's far more specialized than that. It basically computes values of a polynomial from a starting set (interpolate / extrapolate). It doesn't have an explicit fexible divide operation. Exactly what sort of error you get out is going to depend on how you carry out the division, but most likely you would do exp(log(a) - log(b)), which would produce a very large negative number for log(b) (an incorrect result, obviously), and a very large number for the result. It might or might not overflow, depending on the precision of your approximating polynomials for log and exp at the values of interest.
• #### I've done that. (Score:5, Interesting)

on Monday April 14, 2008 @10:50PM (#23073046) Journal
What happens when you divide by zero on a calculator using a physical engine?

I've done that.

The particular calculator in question would spin madly, with the result digit dials working like a cross between an odometer and a clock movement, until you hit the button that aborts the process. (The abort apparently consisted of changing the divisor to a large number. It took close to a minute as the machine would do a trial subtraction, undo it, shift the register bar one to the left, and repeat until it got to the last digit.)
• #### Re:What if... (Score:5, Interesting)

<(moc.liamg) (ta) (egdesuorbenet)> on Monday April 14, 2008 @11:07PM (#23073190)
To start, a famous quote:

"On two occasions I have been asked, "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."

What truly happens to an impossible sum?

Does it dry up

like a slashdotter in the sun?

or does it fester like sco

and then run?

does it stink like an overused meme?

or crust and sugar o'er--

like a deferred dream?

maybe it just sags like a 5-ton calculating machine under a heavy load

or does it explode?

• #### Re: (Score:2)

Perhaps you've drawn excessively from the parent poem in your parody, but I liked this a lot. A fine fusion of literature and geekery. You've earned my admiration (and I've marked you as a friend.)
• #### GIGO (Score:3, Funny)

a famous quote: "On two occasions I have been asked, "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."

I remember reading that one of them was a congressman. If so, things haven't changed in 150 years.

• #### Sounds like a trick question (Score:5, Interesting)

on Tuesday April 15, 2008 @03:53AM (#23074616) Journal
Actually, it is at least possible that it was intended as a trick question. You know, one where if you say "yes" then you've just said "yep, I'm a con artist." Admittedly, it's a stupid one even as trick questions go, but still, there might be some purpose behind it.

To put things into perspective Babbage got funding for one machine, never finished it, decided he's rather begin designing the version 2 model, asked for more funding, repeat ad nauseam. Pretty much it was _the_ original computing vapourware. Pretty soon he got no more funding, but that never stopped him from asking for more and hyping his unproven creation to the parliament.

He also seems to have descended into a nerd-like bitterness, in which he took such questions out of context as proof that everyone else is a drooling idiot and that's why they don't see he's right. And in that he also included such questions as, basically, "well, what _can_ it do?" and "what's the business advantage for making one of these?" Stuff that you'd get asked by any business nowadays too. He took them as proof that his contemporary Englishmen were narrow minded and lacking in vision.

It may seem obvious in retrospect that his design was right, but at the time it was everything except obvious. It was a _monumental_ expense with the economy and technology at that time, even compared to paying armies of people to calculate those by hand. And it was anything but proven. Noone knew if it would even work at all. Again, the first round of funding he got, produced nothing tangible.

Also regarding the parliament at the time, they were not as obtuse as you (or Babbage) seem to think. They funded a lot of research, actually. The nautical clock, for example, was paid for by the parliament, and that was quite the iterative development. The first couple of versions not only were too inexact to be any use, but at least the first one didn't even compensate for the ship's rolling around. But nevertheless, that guy had _something_ working to show for his work, and kept getting more money to keep working. Babbage had nothing except his claims.

Now before I sound too damning to Babbage, it wasn't only his fault. He got into a conflict with the company actually building it, and that was the chief reason why the V1 was never completed. But, still, seen from outside, he never had anything working to show, and even more damning he just unilaterally scrapped the design in the middle of the project and began designing an even more overengineered V2 instead.

So, anyway, given that he was technically hyping vapourware, I can see a smart-arse member of the parliament trying to catch him with a trick question. Again, it _is_ a dumb one, but it's not the same class of dumb as actually thinking that a machine can magically guess the right answers when fed wrong data.

(But then again, I see a ton of PHBs and businesses nowadays believing just that about electronic computers, so maybe it was just a dumb question after all.)
• #### Re: (Score:2)

You get black holes and strangelets.
• #### Pun Engine (Score:2)

What happens when you divide by zero on a calculator using a physical engine?

"Careful, Babbage, you could put out somebody's pi with that thing."

• #### I thought Microsoft already built this... (Score:2)

Does this mean that they are re-releasing Vista? I mean most people consider it a oversized calclator anyway...

(Yes, even Microsoft users can poke fun at themselves too...)
• #### Meh.... (Score:5, Interesting)

<markt@NoSPaM.nerdflat.com> on Monday April 14, 2008 @10:23PM (#23072792) Journal
When you can make an difference engine out of LEGO [woz.org], it really doesn't seem that impressive to build a five ton one. Babbage's analytical engine, however... that would be an interesting piece.
• #### Re: (Score:2, Funny)

Article: Andrew Carol, an Apple software engineer who built a simpler difference engine, entirely of plastic LEGO pieces...

It appears Mr. Babbage should have invented Legos first.

• #### Re: (Score:3, Funny)

Also, synthetic polymers and several artificial dyes.
• #### Re:Meh.... (Score:4, Insightful)

on Tuesday April 15, 2008 @01:02AM (#23073892) Journal
From Carol's site:

Babbage's design could evaluate 7th order polynomials to 31 digits of accuracy. I set out to build a working Difference Engine using standard LEGO parts which could compute 2nd or 3rd order polynomials to 3 or 4 digits
You can compute 3rd order polynomials by hand without too much strain. Seventh order polynomials are too difficult to reliably compute by hand--the mind numbing tedium might get to you after a bit.

Nor can you build a seventh order difference machine out of legos.

Plastic gearing and axles are subject to large amounts of flex and gear lash, which can be a significant problem where any level of precision is required.
Babbage's machine weighs five tons because it was designed to be precise. The museum's machine weighs five tons because it is intended to be a replica of what Babbage created, not just an amusing simplification.
• #### Only the difference engine? (Score:5, Interesting)

on Monday April 14, 2008 @10:36PM (#23072906) Journal
With the money this guy has surely he could afford to build a version of the Analytical Engine. It's not a giant leap for the machinists involved in such a project, given that the fine specifications for the various gears, wheels and cogs is a no-brainer for today's technology -- all the parts could be laser cut by a robot. It would be truly awe-inspiring to see the first computer functioning in all its glory, for indeed it is Turing complete and lays out many of the concepts used in modern digital computers.

[fourmilab.ch]http://www.fourmilab.ch/babbage/ [fourmilab.ch]

The obligatory 99-bottles-of-beer-on-the-wall in punched card Analytical Engine assembly language :

[99-bottles-of-beer.net]http://99-bottles-of-beer.net/language-babbage's-analytical-machine-79.html [99-bottles-of-beer.net]

Hmmm, I dare say that's shorter than the C# version, if you remove the comments. Oh and it will run Linux, if you have enough coal and are willing to wait a few years for X to load. ;) (it does have a graphical output device) As for a beowulf cluster, that might help performance, although your interconnect mechanism would probably be pneumatic ie. tubes (that's what the Internet is made of anyway right?) and the cluster size would require a few tens of millions of units. ;)

jdb2

• #### Re: (Score:2, Informative)

The problem is that there are no complete plans for an Analytical Engine. Drawings and diagrams, yes, but nothing complete. For Difference Engine No. 2, the Science Museum had a (reasonably) complete set of plans. (They had to make a few tweaks, but they did everything they could to keep it in the spirit of the original design.)

Doron Swade's book The Difference Engine: Charles Babbage and the quest to build the first computer is a marvelous read; it was published in the U.K. as The Cogwheel Brain. You may

• #### "History,it seems,is not without a sense of irony" (Score:2)

With the money this guy has surely he could afford to build a version of the Analytical Engine. It's not a giant leap for the machinists involved in such a project, given that the fine specifications for the various gears, wheels and cogs is a no-brainer for today's technology -- all the parts could be laser cut by a robot. It would be truly awe-inspiring to see the first computer functioning in all its glory, for indeed it is Turing complete and lays out many of the concepts used in modern digital computer

• #### Gear jam of death (Score:2)

[a manager grumpily storms into a room full of smoke and dust with gaping holes in the walls and light fittings hanging from the ceiling]
Manager "What happened here I heard this unearthly explosion ? "
[a pallid skinned, slightly chubby man is sitting in the corner wearing shredded clothes and has black burn marks on his face]
BOFH "I tried to port Quake II to the Babage machine and I needed to over clock it a bit and well one of the gears on the number 5 stack jammed when it reached 24,000 rpm"
• #### Picture it (Score:2, Interesting)

Here is the pic of the UK version [sciencemuseum.org.uk].
• #### The login screen (Score:5, Funny)

on Monday April 14, 2008 @11:11PM (#23073224) Homepage Journal

WELCOME TO THE BABBAGE ANALYTICAL TIMESHARING SERVICE

PLEASE NOTE THAT THE INTEGRATOR IS CURRENTLY UNAVAILABLE
DUE TO THE WEEKLY GREASING SCHEDULE. WOULD ALL USERS KINDLY
RETURN ANY UNUSED PLUGBOARDS, AS THE PROGRAMMING TEAM ARE
RUNNING LOW. DIVISION UNIT 3 WILL BE OUT OF ACTION UNTIL
THURSDAY DUE TO EMERGENCY COG REPLACEMENT - PLEASE ENSURE
THAT YOUR PROGRAM DOES NOT ATTEMPT TO DIVIDE BY ZERO AS
THIS CAN CAUSE SEVERE DAMAGE (INCLUDING SHAFT BREAKAGES).
.
.
?
• #### Re: (Score:2)

Bugger. Used all my mod points yesterday :o(

Being British, I'd have liked a reference to the Memory Hole - I'm sure that Mintrue would have run some variant of the Analytical Engine...

• #### I think I speak for everyone when I ask... (Score:2, Funny)

Does it blend?
• #### Re: (Score:2)

Gear smoke. Don't breathe this.
• #### My god why?! (Score:2)

I get the "nostalgia" and "historical interest" thing, but don't waste 5 tons of material doing it! If anything, miniaturize it. It'd be just as cool. Even better? Make an OpenGL version of it and turn it into a screensaver.
• #### Re: (Score:3, Interesting)

I get the "nostalgia" and "historical interest" thing, but don't waste 5 tons of material doing it! If anything, miniaturize it. It'd be just as cool. Even better? Make an OpenGL version of it and turn it into a screensaver.
Personally I'd think it's 5 tons of material well-spent. It was things like these that made me think "How does it work?" when I was a wee lad.
• #### Guess that's why (Score:5, Funny)

on Monday April 14, 2008 @11:27PM (#23073324) Journal
From the FA:

Carol gives the example of multiplying 5 by successive numbers, such as 6, 7, 8. "In simple terms, the method of differences is based on the observation that if the work has already been done to multiply 5 by 5, [then] that work can be reused to multiple 5 by 7 with the addition of another 5 into the previous total," he writes.
I guess that's why the author went into journalism instead of computers.
• #### An idle question... (Score:2)

I don't know how the engine works, but assuming it has the equivalent of adders, registers and some boolean bit-ops, might it be possible to extrapolate the size/weight of a machine such as this that emulates some simple RISC processor of today?

I have visions of a multi-storied, block-sized, brass behemoth, with hundreds of workers scurrying around its innards "de-bugging" (and de-ratting) it, and keeping it lubricated.

Just interested to hear peoples guesses.
• #### See it in action! (Score:5, Interesting)

<larry@portcommodore.com> on Monday April 14, 2008 @11:29PM (#23073346) Homepage
See what one (difference engine #2) looks like running, impressive!

This one is in mechano parts (Erector Set for us Americans)

http://www.meccano.us/difference_engines/rde_2/index.html [meccano.us]
• #### Actual Information - GASP! (Score:5, Interesting)

on Monday April 14, 2008 @11:39PM (#23073388)
I'm am one of the Docents for the Difference Engine #2, and although the team making it work is WAAAAY more competent to comment, lemme put out a few FACTS, at the risk of "flame wars of death"... The Engine is a single function calculator that can iterate the values of a 7th order polynomial approximation to an arbitrary mathematical function. After about an hour of VERY careful setup, any set of coefficients could be entered, allowing almost any function to realized. It uses a technique called "finite differences" that allows the calculation to be performed using only addition (and 10's compliment coefficients to represent negative numbers). Our working plan is to set it up to do a table of logarithms, much like Babbage's own table, produced well before he thought of Difference Engine #2. The polynomial approximation for logarithms is quite accurate over the space from 1.0 to 1.6, 6000 iterations of the Engine. (It takes four turns of the crank or about 6 sec. per iteration.)
The calculation section has about 4,000 parts, and a very elaborate printer mechanism has another 4,000, and was designed to produce sterotype molds of a complete page of a book of tables.
It is a WONDEROUS device to behold! There are 52 distinct stages in it's control graph (EXACTLY like a modern timing diagram, just vertical...) An elaborate nest of 14 cams control the complex sequence of events to do an iteration, which is !pipelined!. The sinuous ripple carry mechanisms on the back side are HYPNOTIC, as are the forward and backward movements of the intra-column sector gears.
Avoid CHM on May 10, it's gonna be a madhouse! But this is pretty close to the top of the list of "1000 Geeky Things to See Before You Die", oh, and by the way, there's all the other ABSOLUTELY WAY COOL stuff at CHM, wanna see an Apple I signed by "the Woz"...
YOU GOTTA SEE THIS! chmguy
• #### How it works (it's not a general purpose computer) (Score:4, Informative)

by Anonymous Coward on Tuesday April 15, 2008 @02:40AM (#23074336)
The Difference Engine is a specialized device which was designed to automate the calculation of tables of values of complex formulae. Such as trigonometric functions, logarithms, etc. The Difference Engine works by using a variant of the Taylor method to approximate complex functions using high order polynomials. It then calculates successive values of the polynomial function using the difference method. It's quite elegant in terms of making the most out of limited computing ability.

Consider a simple polynomial like x^2 + 3*x. Now, take a few initial values of that function like so:

f(0) = 0
f(1) = 4
f(2) = 10
f(3) = 18
f(4) = 28

Now, take the difference between each value where x is increased by the same amount (equivalent to a crude approximation to the derivative of f):

g(1) = f(1)-f(0) = 4
g(2) = f(2)-f(1) = 6
g(3) = f(3)-f(2) = 8
g(4) = f(4)-f(3) = 10

Now do the same with these differences (equivalent to taking the 2nd derivative):

g(2) - g(1) = 2
g(3) - g(2) = 2
g(4) - g(3) = 2

Now we see that the 2nd differences are all the same value, this is because this is a 2nd order polynomial. For a cubic polynomial it takes 3 sets of differences. Now, we can calculate the value of f for x=5 and higher values without the formula by adding the differences.

g(5) = 2 + g(4) = 12

f(5) = f(4) + g(5) = 28 + 12 = 40
f(5) = 5^2 + 3*5 = 40

etc.

We can use exactly the same process to merely approximate functions based on a table of values, given we calculate the differences to a high enough order (i.e. produce a polynomial approximation of high enough order) to give reasonably accurate values. Meaning, taking differences as above to some nth degree from n initial input values and then calculating successive values has the effect of approximating that function with an nth degree polynomial.

Babbage's Difference Engine No. 2 design is capable of calculating 7th order polynomials with 31 decimal digit numbers, which is sufficient to calculate trigonometric and logarithmic functions to very high precision. Using the Difference Engine one would need to manually calculate only 7 initial values, then use the Engine to automatically produce tables for the remainder of the values needed. Compared to the methods of the 19th century (where the term "computer" referred to a person given that job, not a device) this represented an enormous savings of labor, as well as an enormous increase in accuracy of the output, under the right conditions.
• #### It's a pocket calculator (Score:2)

but you have to wear the special trousers.
• #### Size and weight (Score:2)

The parts shown in the photos look pretty hefty, almost large enough to be used in an automotive gearbox. I'd think that good precision machining could make the machine less than 1 cubic foot and a couple hundred pounds, and still be plenty robust. Even smaller if wristwatch-sized gears were used.
• #### What's the difference (Score:2)

between the one in the Science Museum and this new machine? TFS states "two tons heavier", but the article doesn't mention it, nor the CHM website. The London machine weighs 5.5 tons including its printer, the CHM machine also is listed at 5 tons. What gives?
• #### See it while you can-limited time offer (Score:3, Informative)

<hobbes AT xmsnet DOT nl> on Tuesday April 15, 2008 @03:56AM (#23074624)
According to this article [news.com] (which also contains more detail on building and shipping the Engine), the machine will be on display for 6 months, then it will be moved to Myhrvold's home. So if you want to see it, don't wait too long.

(I found another article [wired.com] which claims the Engine will be at the museum for a year. The CHM website doesn't have definitive data.)

I saw the one at the Science Museum a few years ago, and it's awesome. Well worth a trip.

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