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I've been trying to reproduce the output of an analytical machine here at work by doing the calculation myself in Excel but I can't get the error to match. Perhaps I am propagating the error incorrectly...

The calculation is z = 2^(x-y)

The values are:

x = 24.96

y = 25.98

and the std. devs are:

deltax=0.265016

deltay=0.085049

I figured that the error in z should be:

delta z = z * sqrt((2*deltax/x)^2 + (2*deltay/y)^2)

which would give 0.010958

However, the software/machine reports the error as 0.07

I am not 100% sure how the software is calculating the error but it says it uses the standard deviations.

Am I making a mistake in my formula for error propagation? (I haven't done this in a while, frankly).

Any advice much appreciated.

Thanks,

-Alex