Korg Forums

[philtipping]

Ask anyone how to convert degrees C to degrees F and the chances are they’ll try and recall the formula they learnt at school, saying something like: ‘Multiply by 9 and divide by 5, or is it the other way round? Then add 32, or maybe subtract; can’t remember exactly’.
And even if they do remember, the chances are they’d struggle with the mental arithmetic.

I remember media weather reports used to be given in Fahrenheit, and I struggled when they changed over to Centigrade only (or Celsius as the BBC would have it now!); ‘20 degrees’ just didn’t mean anything to me, whereas ‘the 70s’ did (newspapers still use headlines like the ‘sizzling seventies’).

It was many, many years after my schooldays when I learnt of a simpler ‘near enough’ method:
Just double it and add 30
(and the converse: take away 30 and halve it).

I was amazed how easy it was to do in your head, and ever since then I’ve mentally converted (our typical UK) weather temperatures and found them to be within a degree or 2 of the correct answer.

I drew a graph of 'C to F' to help me understand what was happening; the dark blue line uses the exact formula, and the purple line uses the approximate formula.



You can see they coincide when C=10 and F=50, but drift apart either side, so it’s only a good match over a limited range.

This graph shows the actual error between the two formulae, e.g. at C=25, the approx. formula gives a value of F which is 3 degrees too high.



So although it’s no good for scientific use, it’s not bad for getting a gut-feel of everyday weather temperatures (in the UK at least ).
I would be interested to know if this short-cut is common knowledge, and if kids today are told about it. I see no harm as long as its limitations are explained; it would certainly have helped me ‘when I were a lad’.
Phil.

[georgeinar]

i have trouble with this everytime i go to brasil, as it's always around 30 something cent and i can't quite figure out what that means in cent when i'm there
_________________
George Nelson is 2loose
http://www.cdbaby.com/artist/2loose for my cds
http://www.soundclick.com/2loose or follow my tweets = 2loose_buzzgoth (twitter name)

[sweetberry]

very nice information.
_________________
Website counters | Hit counter free download

[philtipping]

Here’s another handy ‘gut-feel’ metric conversion which I never knew at school: cm or mm to inches:-
multiply by 4 (and divide by 10 or 100)

The rule I was taught was 1 inch = 25.4 mm, but I have to confess I'd struggle to do this (and the converse) in my head

I’ve deliberately de-emphasised the divide part as the critical part (for me) is the ‘multiply by 4’. For some reason I have a mental block about the ‘100 or 10’ as I get confused about which one to use, and this highlights the point I made in the first post that if you can’t remember the rules at the time they’re no use!

However in this case we're talking about factors of 10, so by using a mental yardstick (or should that be meterstick?!) you can get in the right ballpark. I know my astronomy telescope has a 100mm diameter mirror as that was how it was described when I bought it. I can visualise this and know it’s 4 inches as opposed to a ridiculous (but desirable ) 40 or 400 inches, so that gives me a gut-feel as to how far to move the decimal point after I’ve multiplied by 4.
You can use whatever you’re familiar with; e.g. a more common reference might be ‘standard’ kitchen units, which are in 500mm widths. These are easy to visualise; you know they’re about a couple of feet across, so when you multiply by 4 and get 2000 you know it must be 20 inches and not 2 or 200 or 2000!

As with the temperature formula this is only an approximation, so here are the graphs to show the limitations.





The error increases steadily as the size increases, but at small 'everyday' values it's not bad, e.g. at 400mm (16 inches), the approximation is only 1/4 inch too big.
Phil.

[Timo]

Inches to centimetres I just multiply by 2.5 (or multiply by 5, then divide by 2).

CM to inches I do the reverse.

Guess at the age of 28 I'm of the digital/metric generation, so I've never used nor needed the quirky Fahrenheit system and don't mourn its loss. Celsius all the way.

Water freezing at 0º, boiling at 100º, easy and relevant to remember (and use), rather than some arbitrary figure.

Mentally to me -2ºC is an icy day, 5ºC is a chilly day, 15ºC is a mild day, 20-25ºC is a very pleasant day, and 30º C is a scorcher.
_________________
[Free Moss Set For All Workstations With Moss Expansion]
[Infekted.org - Original Access Virus Forum & Community]
Trinity V3 PBS | Radias KB | Virus TI Snow | Virus Indigo 1 | 505 Groovebox

[philtipping]

Yes, that's the best approach Timo; eventually these old ideas will fade away as new generations take the new ones in their stride
At double your age I'm afraid I'm still entrenched in the old units; must be my 'core' neural network so guess metric units will never seem 'natural'.
And you're right about the 'ranges'; I do the same thing (but in degrees F), and am not too bothered about the exact scientific value.
Phil.

[Daz]

I am finding this very useful

I moved from the UK where I had been using Celsius all my life and then shifted to using Fahrenheit here in the US when I moved over. At first my first response to reading or hearing summer weather reports in F was that we were all about to boil to death Now having been through all the season, as Timo suggests, I have a mental picture and can associate temp ranges with experience of how those feel. LOL, now on trips back to the UK, I find myself automatically thinking we all going to freeze to death when hearing the numbers

I can't imagine what it must have been like in the UK when everything went from Imperial to Metric measures ... that must have been hellish confusing.

[philtipping]

LOL Daz, just don't get me started on pounds, shillings and pence
Phil.

[Timo]

Think the metric system was made official - or rather the imperial system was made illegal - nearly 10yrs ago here, due to EU regulations forcing us to do so.

There was a national front page news article about a fruit and veg market stall owner making a stand and refusing to sell in kg, sticking to selling in lbs/oz instead, and he was promptly arrested and made to pay a hefty fine or something. It was a complete farce.

The EU has finally backed down over it relatively recently (last year?). They've re-allowed the UK to display both imperial and metric, so long as the metric value is displayed and that the imperial value is not displayed alone, so our Lbs and Pints are safe. Guess it was a bit like the fox-hunting thing, in that it was impossible to regulate as it was part of many people's culture.

I wonder how much money, resources and manpower were wasted in the whole ridiculous debacle!

Can't say I've ever used pounds and ounces in general use. My mum still does. Think the only things I buy in imperial are pints and 5lb bags of spuds.

A person's weight is still actively measured in imperial here though - stones and lbs. And height is still in feet and inches. And longer distances are in miles (including speed being mph). (Shorter distances are in metres, but then feet are used for even shorter lengths than that, followed by inches, and then centimetres, followed by millimetres! So it's very dependant on the range of the thing you're measuring as to what imperial or metric scale you use. Almost like logarithmic mental calibration, rather than bland linear measurements.)

Like Phil with Fahrenheit, it'd be really odd to start using centimetres, kilograms and kph when measuring height, weight and speed respectively, as you've built a mental picture during your life of what they represent and your judgements are based on those, so I can definately see your point Phil!
_________________
[Free Moss Set For All Workstations With Moss Expansion]
[Infekted.org - Original Access Virus Forum & Community]
Trinity V3 PBS | Radias KB | Virus TI Snow | Virus Indigo 1 | 505 Groovebox

[RVNOak]

We're musicians - let's come up with our own scale.

We can measure distances in velocity ranges, measure height in increments of sustain, and weight in series of volumes. We have the right to artistically measure however the hell we want
_________________
We came.
We saw.
We decided to conquer another day...

[X-Trade]

[Timo]

[Rob Sherratt]

If centigrade to fahrenheit is what you want to do, multiply by nine over five and then add thirty two.
If fahreheit to centigrade (to keep up with the times), subtract the thirty two degrees and multiply by five ninths.

[RiotNrrd]

So technically distances can be measured using speed/velocities.

I don't know how it is in other parts of the world, but here on the west coast of the US we do this a LOT.

"How far is it to [some specified location]?"

"Oh, about an hour."

This may be more popularly used in less populated areas, where traffic jams are an uncommon occurrence and drive time is more easily estimated.

[philtipping]