Final answer:
The number of significant figures in a measurement should reflect the precision of the measuring tool, including all certain digits and the first uncertain digit. Zeros may or may not be significant based on their position in the number and the measuring scale used.
Step-by-step explanation:
When reading a scale, the number of significant figures your measurement should contain corresponds to the precision of the measuring tool you've used and your estimated uncertainty. A measurement includes all the digits that are certain, plus the first uncertain digit.
For instance, if a scale displays your weight as "120," then the digits 1, 2, and 0 (even though it's a zero) are all significant figures since they are measured values. Essentially, you should count all nonzero digits, leading and trailing zeros where they serve as placeholders are not counted, zeros between nonzero digits are counted, and decimals indicate precision and are also counted as significant.
When expressing measured values, you can only list as many digits as you initially measured with your measuring tool. The rule for significant figures states that the last digit written in a measurement is the first digit with some level of uncertainty, and the rest are certain.
For example, if you measure something as 36.7 cm using a standard ruler, all three digits count as significant figures. The 7 is the estimated digit, indicating the ruler's limit of precision.