# Find Line Equation from Graphic

Hi,

i'm trying to find the equation for the lines on this chart, my difficulty is with the log scale along the horizontal axis, can you please help?

thanks,
wtc

###### Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Commented:
a line on a log graph
log(y) = a+b*x
would be equivalent to
y = exp(a+b*x) = exp(a) * exp(b)^x

Experts Exchange Solution brought to you by

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Mechanical EngineerCommented:
With all due respect, I disagree about the form of the equation. The X-axis is not linear, so log(y) does not fit a straight line log(y) = A + B*T

The data seems like a better fit for the Antoine equation log(y) = A + B/(C + T)   where A, B and C are constants. http://en.wikipedia.org/wiki/Vapor_pressure
When T is small, the increments on the X-axis would be larger than when T is larger.
Commented:
My answer related to a log scale on the vertical axis, although the question refers to a log scale on the horizontal axis.
But although the vertical axis depicted in the graphic does appear to be logarithmic, the horizontal axis does not.
I agree that it does not appear to be linear in T, but it was not clear from either the question text or the graphic exactly what scale was being used.
Which is why I did not say anything about the relationship between x and T.
A scale of inverse temperature as suggested by byundt does seem to fit x axis better than a linear scale.
###### It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Microsoft Excel

From novice to tech pro — start learning today.