When i integrate the graph, the values seems to be a little

ROOT
1

Hi experts!

I have a problem when i integrate the graph.

Screenshot from 2021-06-06 22-41-02
Screenshot from 2021-06-06 22-41-021563×464 69.3 KB

Even if you look at it roughly, at least 150 looks like it, but the value is only around 111. What went wrong?

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2

Looks okay to me. Just calculate using your favorite calculator:
Integral(65.84*Exp(-0.5*((x-2.815)/0.676)^2), x:=0..6)
The answer is indeed 111.6.

You can additionally check on Wolfram|Alpha: link

3

When fitting the histogram, try to use the "L", or the "I", or both fit options.