# Uncertainty, Accuracy, and Precision Counting is the only type of measurement free from any **uncertainty** (assuming the amount of objects being counted does not change during the process). The numbers of measured quantities, unlike defined or directly counted quantities, are not exact, and thus, **uncertain**. > A measurement’s level of uncertainty depends on the device used (as well as the user’s ability). --- ### Rules of Significant Figure Calculations 1. **When adding or subtracting numbers**, round the result to the same number of decimal places as the number with the least number of decimal places (the least certain value in terms of addition and subtraction. 2. **When multiplying or dividing numbers**, round the result to the same number of digits as the number with the least number of significant figures (the least certain value in terms of multiplication and division). 3. **If the digit to be dropped is 5**, round up or down, whichever yields an even value for the retained digit. > This rule may seem odd but it is based on reliable statistics and is aimed towards avoiding any bias when dropping the digit “5”, since it is equally close to both possible values of the retained digit. # Accuracy and Precision ![[Accuracy vs Precision.png]]