How do you determine the decimal place of the uncertain digit when making a measurement?

The decimal place of the uncertain digit in a measurement is determined by the precision of the measuring instrument used. For example, if a ruler has markings down to the millimeter, the measurement can be recorded to the nearest millimeter, with the last digit being uncertain. Generally, the uncertain digit is one place beyond the smallest division of the measuring tool, indicating the level of precision. Thus, for a measurement of 5.3 cm taken with a ruler, the "3" is certain, and the "0" in the tenths place is the uncertain digit.