Significant figures (commonly called “sig figs”) are the number of figures (digits) included when rounding-off a number.
For example, 789.001 to 6 5 4 3 2 and 1 sig figs is 789.001 789.00 789.0 789 790 and 800 respectively (note the presence and absence of “0”s in 5 4 and 3 sig figs).
By comparison, 789.001 to 3 2 and 1 decimal places is 789.001 789.00 and 789.0 respectively.
The rules about how to round-off are not entirely agreed upon. Basically, when multiplying and dividing given numbers, round-off the result to the lowest number of sig figs given; when adding and subtracting given numbers, round-off the result to the “highest” decimal place given; and use more figures in intermediate steps in a long calculation than in the final result.
Multiplying and dividing:
Round-off the result to the lowest number of sig figs in any of the given numbers.
Adding and subtracting:
Round-off the result to the highest decimal place to which any of the...