Name: The iPhone of Slide Rules - Numberphile
Uploaded: 2020-03-27T18:04:54.000Z
Duration: 8 min 39 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

To-infinitive

I want to talk about slide rules, this is a slide rule, but to explain what it is

So what we have is a classic old school Faber-Castell slide rule. Anyone who is over 50 or

Modal verbs - A2

maybe over 60 would have had to learn to use one of these at school and actually the

use of mathematics for the previous three hundred odd years required the use of

this and you could say that every single scientific invention oh you know through

the age of enlightenment through the nineteenth century and the 20th century

on ease of calculation through use of the slide rule

variety of problems that can be worked with the standard slide rule

so it was shorthand for being a scientist and it's so wonderfully nerdy and I think that

the nerds were like yeah this is this is our this is our sword you know it's a light saber

the way this moves in and out it's so beautifully done this instrument is actually really

pleasurable just going like this here with a slide rule it's not like a calculator

it's not digital you don't get the exact answer you get an approximate answer but

normally within two to three significant figures which

should usually be enough for the job that you're trying to do

we have one of these scales on the top line here "A" which is the top line

we have another identical scale underneath it on "B" so

there are lots of different types of scales here but I'm just going to be using "A" and "B"

"A" is this one here "B" is underneath it

let's say we want to multiply three times four

we look at "A" and we go to where three is

and we put the bottom one at one where three is

then we go up four and then we read where four is on the original one and you can see four is at twelve

just say we do something else as let's say this is something more complicated

seven is a complication number let's multiply seven by seven

and it exactly comes up to forty-nine so that's cool

so what logarithms do and what this is a physical interpretation of

is that they change multiplication into addition

so we're multiplying two things but actually we're just adding two lengths

the reason why this is useful obviously seven times seven we know that in our heads

just say we wanted to multiply 2345 times 6457

we turn that into 2.345 times 6.457 and let's do the sums

that would tell me within a few seconds that 2345 times 6457 is 15 million

this gives us a handy idea of what the answer's going to be

multiplication is addition so division is subtraction

we go to 20 and we basically just need to take away 3

this is something which is quite cool and fun and a bit of a historical relic

but it's not a particularly beautiful thing

unlike my other slide rule my prized possession

ok I'm going to open it is from 1906 and it comes almost like you know

that I'm getting down on my bended knee and giving you a Halden Calculex

so what this is is it is a circular slide rule

here we have the logarithmic scale along a line

in a circular slide rule it's in a circle

this comes with this fantastic sort of set of instructions

the thing is not that many people collect mathematical instruments and so you get probably get loads of

you know this might have been found by someone just clearing out their attic didn't know what it was

like it can't have been more than a few dozen dollars

so revised rules tables and formulae for the Halden Calculex

this is just wonderful absolutely wonderful

price one over six that's a penny isn't it I don't know I'm too young even though I'm old to understand old English

although the ordinary slide rule is usually acknowledged to be a most useful and reliable instrument

for instance it is a most inconvenient article to carry about in one's pocket

also in the hands of the average user it is rendered almost useless for any unusual calculation

so in other words you couldn't put this in a pocket and it's not very elegant

on the other hand the Halden Calculex is beautiful it's like a pocket watch

and it's something that if you ever needed to do fast approximate analogue calculations on the fly

you're moving this logarithmic scale against the top one so two sides

so again there are lots of different scales for doing lots of different things

I'm just going to concentrate on multiplication and division