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I am not a mathematician(IANAM), however I wish I could be.

My question: I often find this at the bottom of pages.

Page generated in 0.00013899803161621

Sometimes, I come across

Page generated in 9.0122222900391E-5

What does that time mean?

I tried searching Wikipedia for E and maths but found the e mathematical constant with a scary looking graph. My guess is E stand for Exponential or something and -5 is the power it is raised to. And the time is a really small number. But that doesn't make sense when compared to the other time in the question is 0.00013899803161621 bigger than 9.0122222900391E-5?

If it means x times $10^{-5}$, then 9.0122222900391E-5 will be 0.000090122222900391 which is smaller than 0.00013899803161621

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In case anyone knows: where is this particular number coming from? There are a large number of google hits for it, many of which are not mirrors of this site, whereas (unsurprisingly) if I change the last decimal place by 1 in either direction there are no hits at all. – Michael Lugo Aug 25 '11 at 23:21
@Michael, for whatever it's worth it is the multiple of $10^{-18}$ that is closest to $189\times 2^{-21}$. Google also knows various multiples of $2^{-22}$ to a similar precision. They all seem to be values related to timing. Possibly related, I have come across a bug in some versions of Linux whereby the system time would be off by exact multiples of $\frac{2^{42}}{10^{9}}$ seconds. Notice that $42+22=64$... – Henning Makholm Nov 12 '11 at 20:37
So it is really a computer question, not a math question. If you want something other than wild speculation to the supplementary question "what does the E stand for?" you should try a computer site... – GEdgar May 8 '12 at 12:00
How in the world does this have 12K views? – user641 Mar 12 '13 at 1:37
How does this page have 125K views now?? – Nayuki Dec 28 '15 at 5:32
up vote 41 down vote accepted

It means $9.0122222900391\times 10^{-5}$. It's known as "scientific notation".

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Is the E an abbreviation for something? – Rasmus Oct 7 '10 at 16:29
On calculators that E is sometimes denoted "exp", which is short for "exponential". In fact, "exponential notation" is another name for "scientific notation" – Andy Oct 7 '10 at 16:33
Well, only mathematicians the following is true: "Thou shalt not have another base before e", right? ;) – Andy Oct 7 '10 at 16:59
@AD.: I was really confused for a while, until I realized that you meant $\log_{10}$ rather than $\log_1 0$. :-) – Hans Lundmark Oct 8 '10 at 11:28
@Hans Lundmark: Of course, sorry :) – AD. Oct 9 '10 at 4:41

E-5 just means x 10^(-5) i.e. divided by 100000

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I have always taken the E or e to mean "exponent of 10." This construction parses in all modern computing languages as an IEEE754 double or single precision number.

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protected by MJD Oct 19 '13 at 6:44

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