Log10 Trendline in Charts

Greg73

New Member
Joined
Aug 5, 2010
Messages
2
Does anybody know if it is possible to get Excel to calculate a logarithmic trendline in a chart using base 10 and not base e?
 
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Cindy Ellis

MrExcel MVP
Joined
Jun 9, 2006
Messages
1,802
Hello, and Welcome to the Board!

As far as I know it's not possible. If you need the log10 trendline equation, your best bet would probably be to calculate the log10 of the x axis in a helper column, then use the slope and intercept worksheet functions to calculate the coefficients. The form of the equation would be Y = slope * log10x + intercept.

Hope that helps,
Cindy
 

pgc01

MrExcel MVP
Joined
Apr 25, 2006
Messages
19,885
Hi Greg
Welcome to the board

Isn't the trendline the same? I think it's only the coefficient of the logarithm in the equation that changes.

As you know if you divide the logarithms of any number in 2 different bases you get a constant. You can therefore replace the logarithm in a base by the logarithm in another base just by multiplying by that constant.

Ex. You display the trendline equation in the chart:

y = 675.489569563135 * ln(x) - 224.580147323782

We know that

ln(x) = ln(10) * log(x) = 2.30258509299405 * log(x)

Replacing, we get

y = 1555.37221334904 * log(x) - 224.580147323782

Is this what you want?


Remark: I used the names of the worksheet function, ln(x) for logarithm of x in base e and log(x) for logarithm of x in base 10.
 

Greg73

New Member
Joined
Aug 5, 2010
Messages
2
Thanks Cindy for confirming its probably not possible.

You are right pcg01, I could calculate the correction to make it log10 for use in calculations if i want to, but I was hoping for presentation purposes to have it appear as log10 on the chart.

Cheers.
 

pgc01

MrExcel MVP
Joined
Apr 25, 2006
Messages
19,885
You are right pcg01, I could calculate the correction to make it log10 for use in calculations if i want to, but I was hoping for presentation purposes to have it appear as log10 on the chart.

If you want to have it appear with Log on the chart why don't you just edit the equation?

In the example I presented the equation on the chart was

y=675.489569563135ln(x)-224.580147323782

and you'd replace it with

y=1555.37221334904Log(x)-224.580147323782

Isn't this what you want?
 

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