# don't know how to read the log chart

Discussion in 'General Electronics Chat' started by sumalama, Nov 20, 2014.

1. ### sumalama Thread Starter New Member

Nov 19, 2014
4
0
Hello,

can anybody tell me how much value is the red line (point on x axis) is indicating in the figure attached?
its confusing me.

thanks

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2. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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It looks to me like the line is about half way between $1X10^{^{-4}}$ and $2X10^{^{-4}}$ . Since on a log chart, half way is about 3, not 5 (i.e., 10^1/2 =3.16...), I would say the line is $1.3X10^{^{-4}}$.

John

3. ### sumalama Thread Starter New Member

Nov 19, 2014
4
0
i thought it was 9.5*10^-3

so, what is it for sure?

4. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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I thought it was homework. The chart reads left to right, the value has to be less than 10^-3.

John

Edit: If you can find an old slide rule at a museum, you can see what I mean.

Last edited: Nov 20, 2014
5. ### wayneh Expert

Sep 9, 2010
12,144
3,054
Your's is. One could quibble over the last significant figure, but I agree with your estimate.

6. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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Well, since the mark was in crayon, I didn't try to be too accurate. Besides, it is not often today that you can go back to your old Pickett skills.

In reality, my intent was to help the TS analyze the question.

John

7. ### MrChips Moderator

Oct 2, 2009
12,447
3,362

So it is somewhere between 0.0001 and 0.001
The next mark to the right represents 0.0002
Hence it is somewhere between 0.0001 and 0.0002

Now look at a slide rule which uses a log scale:

The cursor is positioned halfway between 0.0001 and 0.0002
Hence I call it 0.0001414

Virtual Slide Rule

Last edited: Nov 20, 2014
8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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I must have been asleep earlier. The range to consider here is not 1 to 10, but rather 1 to 2. I agree the answer is 1.4142... for the half way point.
John

Last edited: Nov 20, 2014
9. ### wayneh Expert

Sep 9, 2010
12,144
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I saw it as not quite halfway, hence 1.3. But upon further review, it is indeed halfway. 1.4 it is.

10. ### sumalama Thread Starter New Member

Nov 19, 2014
4
0
thank guys

ans = 1.414*10^3

11. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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That exponent cannot be right based on the image you posted. Is there more to that image?

John

12. ### sumalama Thread Starter New Member

Nov 19, 2014
4
0
oh sorry, i meant

ans = 1.414*10^4

no there is nothing more to the image

13. ### wayneh Expert

Sep 9, 2010
12,144
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Four significant figures? Your eyes must be better than mine.

14. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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The value exactly halfway (as discussed above) between 1 and 2 is 2^1/2 . My earlier error was a brain lapse, and I was considering the range between 1 and 10.

John

15. ### wayneh Expert

Sep 9, 2010
12,144
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Yes, but "exactly" is judged by eyeing a crayon mark, and that judgement doesn't warrant 4 sig figs.