Help with calculating the speed of a muon using change in muon flux and altitude I have been trying to calculate the speed of a muon using the change in muon flux and altitude using Lorentz transformations. This website explains the process with an example: Example of Muon Experiment.
Unfortunately, this method isn't working with data from other sources like this graph:

This is the source for the graph: Flux Variation of Cosmic Muons
It should yield a speed of about 99% the speed of light, but it is instead completely off. No matter which change in altitude and change in flux I use from this graph, I get an incorrect answer, and I don't know why. Is the data flawed or am I misunderstanding the math? Should I use a different method? I would greatly appreciate any help.
The example on the website has 2 muon fluxes of 422 and 550 muons per minute and a change in altitude of 1219. This is the solution:


Combining both steps, I got the equation:

Where h is the change in altitude, f is the flux corresponding to the lower altitude, and F is the flux corresponding to the higher altitude. This formula works for the values provided by the website, but doesn't work for any values I tried from the graph above such as a change in altitude of 441 m between the rightmost bar and the 2753 ft bar and the corresponding fluxes of about 2400 and 750. Thank you to anyone who can provide any help.
 A: Welcome to stackexchange.

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*Does the data fit the simple exponential you assume? The simple exponential is only right if all else is equal: atmospheric density the same, shielding the same, background level the same, etc. Also, the  interaction probabilities need to be negligible throughout.

That is unlikely to be the case for any real data across such a vast range of altitudes. Underground you will have shielding. Your background in your detector will be vastly different, since the hadronic component in cosmic rays varies with altitude, plus underground, there is radioactivity from the rock too. Depends on your detector whether that impacts the data or not.
Thus, let's approximate:

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*Do you get a right-ish answer when you use only two neighboring numbers (e.g. at 338ft and 2753ft, etc.)?

A: The data look quite strange to me. I assume -60 ft is underground, thus shielded and irrelevant. The huge difference between 2735 and 4200 ft tells me that something other than altitude is involved here, too.
