Slope and Intercept Formula Issue

[DrPainPhD]

Hello, all,

I am having an issue with the calculation of my Y-intercept for a fit model I am generating. The graph is in lin/log format (Y axis is linear while X axis is Log10).

For one example graph, here are the data for X and Y coordinates:

X=0.00024, 0.0008, 0.0024, 0.008, 0.024, 0.08
Y=0.0002959, 0.011835, 0.045136, 0.268209, 1.694904, 12.247465

When I use the SLOPE formula I get 3.797433 and INTERCEPT gives me 11.33409 (using the Log10 of the X value range)

Calculating by hand my SLOPE is correct, but I get 10.99 as my INTERCEPT. Can someone tell me the formula that Excel is using, because that is a big enough difference that calculation values from the curve end up wrong enough to impact my results. Which is correct (I assume 11.33 is).

 

[pgc01]

Hi
Welcome to the board

Check the help for the functions. It has the formulas that excel uses and you can compare with yours.

 

[shg]

Try applying a power function trendline -- it's a good fit to the data (it's linear on a log-log plot).

If you want the coefficients on the sheet, you can use =linest(ln, ln(x))