After the Cl

^{-} determination in a bottle of water using IC and a calibration method I get:

X= 3,1786 mg/l

S calc. ("standard deviation") = 0,224780537 mg/l

Now I have to express the analitical data:

X ± t * S calc

3,1786 mg/l ± 0,484960449 mg/l

Have to approximate the uncertainty ""± 0,484960449 mg/l"" at the first non-zero term ??

Reading the J.R. Harrys usually the uncertainty is approximated at the first non zero term....

In this case I get:

0,5 mg/l....

THANKS