Two Y axis with different scales for a line chart

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vacaut - 29 Oct 2003 15:29 GMT

I have to plot a line graph with two Y axis. The primary Y axis is
normal scale ranging from 10 to 60 with interval of 10. The secondary Y
axis needs to correspond to the primary axis but in log scale, i.e.
from log10 to log60 with interval of log10.

This question actually comes from a request to display the same data in
different unit. Primary axis displays the data in Watt, whereas the
secondary axis using db, which is log scale.

I have tried to create a dummy series, but find it difficult to align
the two y axis. Also, excel does not seem to be able to display a
maximum of log60.

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dvt - 29 Oct 2003 16:13 GMT

> I have to plot a line graph with two Y axis. The primary Y axis is
> normal scale ranging from 10 to 60 with interval of 10. The secondary Y
[quoted text clipped - 8 lines]
> the two y axis. Also, excel does not seem to be able to display a
> maximum of log60.

As you probably know, it will be impossible to align the intermediate tics
on these axes. I can't quite understand what you mean when you say you
"find it difficult to align the two y axis."

Excel does not allow you to stop or start a log chart at anything but
integer powers of 10 (1, 10, 100, ...). So you can't use the default
settings to stop at log60. But there is a workaround. See
www.tushar-mehta.com, Flexible Log Scale on the left side of the page.

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Dave
dvt at psu dot edu

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pl.carry - 29 Oct 2003 17:56 GMT

For alignment of ticks, if I understand you well, all you need is to ensure
that you chose (widen always) the right and left ranges so that when you
divide them by the tick step left and right you obtain the same integer.
Best is an example:
Range 1 is 140 to 700
Rang 2 is 30 to 50
Force range 1 to 100-700, that is 6 steps of 100
Force Range 2 to 25 to 55, that is 6 steps of 5
Your ticks will align and any horizontal line will serve for both.
HTH,
Pierre
On Wed, 29 Oct 2003 09:29:35 -0500, vacaut
<vacaut.w2eo2@excelforum-nospam.com> wrote:

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Dave
dvt at psu dot edu

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vacaut - 30 Oct 2003 13:36 GMT

Thanks Dave for the website. When i say "align the two Y axis", i
actually means that ticks on the two Y axis are in the same horizontal
line. E.g. draw a grid line, left intersection with primary Y axis is
20, right intersection with secondary Y axis is log20.

I just realized that what i really need is the ability to put Y ticks
at arbitary interval (in this case, log scale interval), not
necessarily to make the secondary Y axis into log scale.

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dvt - 30 Oct 2003 14:36 GMT

> Thanks Dave for the website. When i say "align the two Y axis", i
> actually means that ticks on the two Y axis are in the same horizontal
> line. E.g. draw a grid line, left intersection with primary Y axis is
> 20, right intersection with secondary Y axis is log20.

I'm not completely sure what you mean. It would be impossible, for
example, to line up tick marks for 10, 20, and 30 with tick marks for
log(10), log(20), and log(30). That's not a limitation of Excel; you just
can't do that mathematically.

> I just realized that what i really need is the ability to put Y ticks
> at arbitary interval (in this case, log scale interval), not
> necessarily to make the secondary Y axis into log scale.

Try
http://www.geocities.com/jonpeltier/Excel/Charts/DummySeries.html#ArbAxis.

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Dave
dvt at psu dot edu

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