The rules for significant figures that we will be following are those outlined in Felder and Rousseau, Elementary Principles of Chemical Processes (Wiley, NY: 1986), the text for CM204/CM205. Briefly stated, they are as follows:

1. All non-zero digits are significant. (2.3, 22, and 120 all have two significant figures)
2. Zeros between non-zero digits are significant (203 and 1.02 have three significant figures).
3. If a decimal point is present, all zeros to the right of the decimal point are significant (1.000 and 23.20 have four significant figures).
4. Whole numbers that are part of the physics of an expression are infinitely precise (the 2 in the expression for the circumference of a circle, 2pR, has an infinite precision since it expresses the fact that twice the radius is the diameter). Numbers written as whole numbers which are experimentally derived, however, follow the rules above (e.g. the height of a column of fluid given as 2 inches has one significant figure)
5. Whole numbers that describe a number of discrete objects (e.g. 17 peaches) have an infinite precision.

1. "When two or more quantities are combined by multiplication and/or division, the number of significant figures in the result should equal the lowest number of significant figures of any of the multiplicands or divisors." For example (1.0)(120) has two significant figures; (31)(2.34545) has two significant figures.

When two or more numbers are added or subtracted, the positions of the last significant figures of each number should be compared. Of these positions, the one farthest to the left is the position of the last permissible significant figure of the sum or difference." For example (12-1.0034)=10.9966 should be written as 11, i.e. has two significant figures.


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