What determines the significant figures in a measurement?

The determination of significant figures in a measurement revolves around the concept of which digits contribute to the precision of that measurement. Significant figures include all the digits that are known with certainty and one final digit that is estimated. This means any non-zero digit, any zeros between significant digits, and trailing zeros in a decimal number are all considered significant.

Therefore, when a measurement is taken, every counted digit (those that are explicitly known) and estimated digit (those that contribute to the precision) are included in the total number of significant figures. This approach provides a clearer understanding of the measurement's accuracy and reliability. An example is measuring a length as 12.3 cm; here, all three digits are significant because they give important context about the precision of the measurement.

In contrast, other options do not accurately define significant figures. For instance, stating that only whole numbers or only measured digits count fails to encompass all important aspects needed for precise scientific communication. Rounding all digits to the nearest whole number would disregard the valuable information contained in decimal places that could signify important details about measurement precision.