I I'm confused on which equation gives percentage uncertainty

AI Thread Summary
The discussion revolves around confusion regarding which equation to use for calculating percentage uncertainty in the context of finding the best fit line through data points. Two different methods for determining slope are mentioned, with one relying on visually drawing lines and the other assuming a known best line. The choice of equation depends on the method used to derive the best fit line. There is also a focus on understanding the statistical context of the slopes being analyzed, including the importance of units in determining percentage versus absolute uncertainty. Clarity on these points is essential for accurate uncertainty calculation.
homeworkhelpls
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im confused about the difference of this equation:
1665243195922.png

and this one:
1665243195935.png

which gives percentage uncertainty, so which one should be used to calculate the uncertainty?
 
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Are you trying to compute the average gradient?

or are you trying to find the best line through a set of data points plotted in XY form?
 
my bad I am trying to find the uncertainty from the graph
 
The two equations are out of context but my guess is that they refer to different methods of determining the slope (gradient). It looks like the second equation assumes that one knows the best line (determined how?) while the first equation assumes that one draws two eyeballed straight lines that pass reasonably well over the data such that the best line has a slope between them. Which one you use depends on your method of finding the best line.
 
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kuruman said:
The two equations are out of context but my guess is that they refer to different methods of determining the slope (gradient). It looks like the second equation assumes that one knows the best line (determined how?) while the first equation assumes that one draws two eyeballed straight lines that pass reasonably well over the data such that the best line has a slope between them. Which one you use depends on your method of finding the best line.
no sorry bro i don't think you understand it very well i mean the uncertainty and best fit is just determined by drawing the line, thanks for the help though
 
It almost certainly looks like a simplified procedure that likely overestimates the uncertainty.
 
homeworkhelpls said:
which one should be used to calculate the uncertainty?
I assume that you mean the standard uncertainty of the slope.

You have not provided enough information. What do these max and min slopes represent? Are they slopes from a 95% confidence interval around the fitted slope parameter. Are they slopes takin men directly from the data? Do you have any other estimate that could describe the statistical distribution from which these slopes are drawn?
 
Hint: Think about the units.

What units would you expect a percentage uncertainty to have versus an absolute uncertainty?
 

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