Guidance on Significant Figures and Rounding of Result.

In Pharmaceutical Industries, it's is very important to know the guidance for significant figure and rounding of results.
USP and ICH has given some guidance on this topic.
The drug analyst should be thoroughly familiar with thease topic.
Some highlights on this topic are summarized below-

1. Numerical limits specified in a monograph include the extremes of the values and all values in between, but no values outside these limits.
This statement should be applied after proper rounding of numericalr results, for example, a properly rounded result is found to lie exactly
at the extreme of a limit .
(e.g. limits 98.0-102.0% of declared; found
102.04%, rounded to 102.0%) then the monograph limits are met. If the
result lies outside the numerical limits (e.g. 98.0-102.0% of declared;
found 102.05%, rounded to 102.1%), then the monograph limits are not met.

2. Numerical result should be reported to the same number of decimal
places as the limit expression stated in the monograph. For example, if
limits are stated as 90.0-110.0% of declared, report results to 1 decimal
place (e.g. 98.3%, 101.8%), after applying USP rounding rules.

3. The USP has slightly different rounding rules:
USP rounding conventions are as follows:
a. Retain only one extra digit to the right of the rightmost digit of the monograph limit expression.
b. If the extra digit is less than 5, drop the digit.

c. If the extra digit is greater than 5, drop it and increase the previous digit by one.

d. If the extra digit is exactly five, then drop it and (always) increase the
previous digit by one.

4. An explicit statement is made for titrimetric procedures: essentially all
factors, such as weights of analyte, should be measured with precision
commensurate with the equivalence statement given in the monograph.
Examples in the significant figures section above illustrate the
importance of this for all analytical work.

Few examples are given in the following -
For Assay:
If limit is 95.0 to 105.0%.
Result-1: 94.94%----Reporting as per rounding rule:94.9%----Doesn't comply. 

Result-2: 94.95%----Reporting as per rounding rule:95.0%----Complies.

For Related Substances:
If limit is NMT 0.20%.
Result-1: 0.206%---Reporting as per rounding rule:0.21%----Doesn't comply. 
Result-2: 0.203%--Reporting as per rounding rule:0.20%---Complies.

If limit will 0.2% instead of 0.20%, then both the cases are complying to the specification.