Basic standard deviation calculation

[Graham87]

I don’t get how they got the equation for the standard deviation. Why do they only square with the time in the denominator?

Thanks!

 

[gleem]

We know that the SD of the total number of counts n is √n and rate r =n/t

So;
n=rt
Δn = (Δr)⋅t =√(n/t)t
Δr=√(n)/t =√(n/t²)

 

[Graham87]

We know that the SD of the total number of counts n is √n and rate r =n/t

So;
n=rt
Δn = (Δr)⋅t =√(n/t)t
Δr=√(n)/t =√(n/t²)

Aha! Thanks!