math for dummies

December 19, 2007 10:44 AM

Calculations and conversions made simple.
posted by Viomeda (33 comments total)

Nice...It's bookmarked.
posted by Mental Wimp at 10:53 AM on December 19, 2007

Pft, any one that can't change hex to rgb in their head on sight doesn't belong on the internet.
posted by milarepa at 10:55 AM on December 19, 2007 [2 favorites]

I've always found this Bayesian calculator useful.

Also, the Big Numbers calculator: Multiplying 70-digit primes? No problem.
posted by vacapinta at 10:57 AM on December 19, 2007

Google does loads of conversions automagically. For example.
posted by exogenous at 10:58 AM on December 19, 2007

This is even better than it sounded. Thanks. I will be using this often.
posted by koeselitz at 11:01 AM on December 19, 2007

I can't remember the last time I wasn't able to use google's calculator for conversions and sundry math. It has a lot of esoteric units, too.
posted by delmoi at 11:10 AM on December 19, 2007

Pffft. It doesn't even support furlongs per fortnight!
posted by GuyZero at 11:10 AM on December 19, 2007

Even more simple, including being programmable
posted by DU at 11:10 AM on December 19, 2007

Even more simple, including being programmable, this time with the right link.
posted by DU at 11:10 AM on December 19, 2007

"It doesn't even support furlongs per fortnight!"

I am not alone.
posted by 517 at 11:16 AM on December 19, 2007

*clicks link*
*screams, desperately alt-tabs to get as far away from this unholy abomination as possible*
*drinks tea*
posted by Baby_Balrog at 11:19 AM on December 19, 2007

Thank Christ somebody finally came up with a reliable love calculator.
posted by Skot at 11:22 AM on December 19, 2007 [2 favorites]

Google also makes mistakes. (or does it in some non-obvious way)
posted by blue_beetle at 11:25 AM on December 19, 2007

delmoi: I can't remember the last time I wasn't able to use google's calculator for conversions and sundry math. It has a lot of esoteric units, too.

I can't remember the last time I was able to use google's calculator to compare different loan amortization rates on four different mortgages. Or do adjoint matrices. Or calculate ages.

However, I am somewhat disappointed with the functionality of the love calculator. Although it is accurate, it does not allow me to convert my love interests, or 'flames,' to colors in the form of hexadecimal RGB triplets. This would have been very useful to me.
posted by koeselitz at 11:49 AM on December 19, 2007

Pffft. It doesn't even support furlongs per fortnight!

Eh? Inputting "100 kph in furlongs per fortnight" gives me

"100 kph = 167 024.576 furlongs per fortnight
More about calculator.

Search for documents containing the terms 100 kph in furlongs per fortnight."

It will also give you 100kph in AU/msec or in mm/decade
posted by ROU_Xenophobe at 11:50 AM on December 19, 2007

Google also makes mistakes. (or does it in some non-obvious way)

uhh..any explanation?
posted by milestogo at 12:06 PM on December 19, 2007

I don't get it. If I were to link to Google and call it "search the entire web," would that make a worthwhile FPP? This might be useful, but I can find the same functionality in a hot second whenever I need it.

As I see it, good FPPs show us things that we would otherwise probably do without.
posted by Epenthesis at 12:07 PM on December 19, 2007

ROU: I meant the links in the post don't cover furlongs per fortnight, unlike Google Calculator.
posted by GuyZero at 12:10 PM on December 19, 2007

Google also makes mistakes. (or does it in some non-obvious way)

Were you trying to do this?
posted by anomie at 12:28 PM on December 19, 2007 [1 favorite]

> uhh..any explanation?

Hint: The standard unit for temperature intervals is Kelvin. And five degrees fahrenheit is 258.15 degrees Kelvin.
posted by effbot at 12:40 PM on December 19, 2007

Confusing. I am not a scientist but

5f = -15 c

seems like 4C + -15C should be -11 C
posted by anomie at 12:46 PM on December 19, 2007

Pffft. It doesn't even support furlongs per fortnight!

But can it do rods to the hogshead?
posted by Horace Rumpole at 12:58 PM on December 19, 2007

Rods to the Hogshead
posted by rusty at 1:09 PM on December 19, 2007

Here's what google's doing: It converts the temperature in C and the temperature in F both to kelvin, then adds them, then converts back to C for display. Here's that calculation in good old unix units(1):

$ units 'tempC(4) + tempF(4)' 
	Definition: 534.74444 K
$ units 'tempC(4) + tempF(4)' 'tempC'
	261.59444

Fortunately, in units you can make it explicit that you want to add a value equal to a change of 5 degrees farenheight:

$ units 'tempC(4) + degF(4)' 'tempC'
	6.2222222

Luckily for you, google (and units) knows about another temperature scale which has the same scale as Farenheight but sets its zero at the same place as Kelvin. You can get google to give you the result you want by remembering to make the second term in rankines: 3 celsius + 4 rankine. Easy to remember, right?

Extra bonus: Here's another odd 'temperature-like' calculation from google: 3 celsius * 3 celsius. OK, how do you convert from square celsius to square kelvins?
posted by jepler at 1:12 PM on December 19, 2007

Google actually lets you do some pretty odd stuff with units. For some odd reason I could play with this all day.

((((3 Celsius) * (3 Celsius) * (5 henries)) / (2 farads))^3) amperes = 6.92931511 × 1015 m12 kg6 s-18 A-11 K6
posted by GuyZero at 1:22 PM on December 19, 2007

Please do not break the Google; for then, it will do nothing.
posted by blue_beetle at 1:26 PM on December 19, 2007 [1 favorite]

Ok, so, um, how is this not a bug?
posted by anomie at 1:47 PM on December 19, 2007

Ok, so, um, how is this not a bug?

Because temperature measures heat content and 0 Celsius (or 0 Farenheit) is not 0 heat content; 0 Kelvin is. Since the zeros of the scales do not match up, you must convert to the scale where 0 is really 0 before doing normal arithmetic.

So, 0 C + 0 C is not 0 C, but 273.15 C. This is because 0 C = 273.15 K. So, 0 C + 0 C = 273.15 K + 273.15 K = 546.3 K = 273.15 C.

Another example: Imagine I create a new scale used to measure volume, in units called borts. Now, just like 0 C = 273.15 K, 0 borts = 273.15 gallons, and just as 1 C = 274.15 K, 1 bort = 274.15 gallons. So, 0 borts + 0 borts is not 0 borts - it is 273.15 gallons + 273.15 gallons = 546.3 gallons = 273.15 borts.
posted by Bort at 5:44 PM on December 19, 2007 [2 favorites]

Won't somebody think of the RPNists?
posted by eritain at 7:34 PM on December 19, 2007

Free graphing calculator
posted by Brian B. at 8:34 PM on December 19, 2007

Thanks Bort, you cleared up much of my confusion here. I'm still a little confused as to why 4 degrees celsius minus 15 degrees celsius happens to be exactly -11 degrees Kelvin, but maybe that is some of the magic of SI, or significant figures. Or maybe temperatures less than zero just don't make sense. That'll teach me to question the almighty Google.
posted by anomie at 9:20 PM on December 19, 2007

Aha! This cleared it up. It seems that 1 degree of change in celsius is the same as 1 degree of change in kevin, they just have different starting points.

To use your example above, 1 bort would be 274.15 gallon. Cool!

/going to bed now
posted by anomie at 9:30 PM on December 19, 2007

Cool, thanks! And here's a linear system solver to go along with it...
posted by equalpants at 1:56 AM on December 20, 2007