Error 误差

delta x=2cm

delta y=2cm

• if the two uncertainty are independent, the error of

z=x+y

will be

delta z=sqrt(2^2+2^2)=2.8 cm

the mean value of  x and y has an error of 

delta mean=2.8/2=1.4 cm

• if you suspect the uncertainties may not be independent, the

error will be
delta z=2+2=4 cm

the mean value of  x and y has an error of 

delta mean=4/2=2 cm