[xshadow]

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