Error Analysis: Addition of Quantities with Uncertainty

[NachoNovo]

Hi there,

I have a pretty basic question on error analysis. say we want to obtain a quantity which is given by u+v.

if u = 8.5452545 and has uncert 0.025454. it would be quoted as 8.55(2) and if v = 3.865898 and has uncert 0.04124343.

it would be quoted as 3.87(4).

but when calculating say u+v...

do i a) use 8.55 and 3.87 and their rounded uncertainties.

or b) use the raw data?

thanks for any help.

 

[technician]

The uncertainty of a given value must be in the last significant figure.
So if u is given as 8.5452545 the uncertainty is in the last figure 0f 5.
It means that u lies between 8.5452544 and u = 8.5452546.
This is what is meant by SIGNIFICANT figures.
Hope this helps

 

[NachoNovo]

no sorry it doesn't help.

I'm not sure when calculating a new value experimentally if I use the rounded values or the raw values of the old data?

I know what sig figs mean.

 

[technician]

where did these figures come from?
Are they from a question you have seen?
Were they given to you to test your understanding?
Are they values you have measured?

 

[NachoNovo]

The values are made up. I am writing up a report and wasn't sure what to do.