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

 Chart
WTC_ServicesAsked:
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ozoCommented:
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
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byundtMechanical 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.
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ozoCommented:
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.
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