Here's how it relates to significant figures:
* Significant figures are digits in a number that are considered to be reliable and contribute to the precision of the measurement.
* Doubtful digits are the digits that are uncertain and are not considered reliable. They usually represent the last digit in a measurement, which is estimated by the observer.
Example:
Imagine you are measuring the length of a piece of cloth with a ruler marked in millimeters. You see that the cloth ends between 12.3 cm and 12.4 cm. You might estimate the length to be 12.35 cm.
* Significant figures: 1, 2, and 3 are significant figures, as they are certain.
* Doubtful digit: 5 is the doubtful digit, as it is an estimate.
Important Note: The term "doubtful digit" is not commonly used in scientific writing. It is more common to use the term "uncertainty" or "error" to refer to the level of doubt associated with a measurement.