Calculating value on a trendline

[Y Cheong]

Hi

I have a set of points and have got a trendline using
these. Is there a way of finding a value of x for a
certain value of y? The only way I can do it is by getting
the equation of the line and then trying out different
values of y, until I get an x value.

However the strange thing is that when I get a set of
values using this equation and try and plot this trendline-
I should get the same trendline as before as the equation
is the same, however this is not the case!! Has anyone
else come across this strange phenomenon??!!

Y

 

[Bernard Liengme]

This 'strange phenomenon's is due to lack of precision. The Trendline
equation may display (for example) 1.23 but the actual stored values may be
1.2565786. When these two number are multiplies by X^4 (generally a large
number) different values result.
The solution is (a) to format the trendline equation so as to display more
digits and to copy all of these into your formula, OR to use LINEST in the
form =LINEST(y-values, x-values ^{1,2,3,4,5,6}). See my website for more
details.

Best wishes
Bernard
www.stfx.ca/people/bliengme/ExcelTips

 

[Bernard Liengme]

This 'strange phenomenon's is due to lack of precision. The Trendline
equation may display (for example) 1.23 but the actual stored values may be
1.2565786. When these two number are multiplies by X^4 (generally a large

number) different values result.

The solution is (a) to format the trendline equation so as to display more
digits and to copy all of these into your formula, OR to use LINEST in the
form =LINEST(y-values, x-values ^{1,2,3,4,5,6}). See my website for more
details.

Best wishes

Bernard

www.stfx.ca/people/bliengme/ExcelTips

 

[Guest]

Bernard

Thank you very much for this.

Is there a way of pointing to a value on the trendline and
getting both the x and the y values?

Currently I am putting in the minor gridlines and judging
using these.

Thanks
Y