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Discussion

To find the scale increment, subtract the values of any two adjacent labeled graduations and divide by the number of intervals between them. For the thermometer shown, first subtract 90 °C - 80 °C = 10 °C. Next, count that ten intervals are between the labeled graduations. Therefore, the scale increment is 10 °C/10 graduations = 1 °C/graduation.

The graduations are used to find all of the certain digits. Since the last labeled graduation below the meniscus is 80 °C, we know that the temperature is greater than 80 °C,. Next, use the scale increment. There are seven graduation marks below the meniscus, and each graduation represents 1°C, so the certain digits of the reading are 87 °C.

The final digit is uncertain and must be estimated. Estimate the distance that the meniscus lies between the two graduations as a decimal fraction and multiply by the scale increment.

The bottom of the meniscus is about seven tenths of the way between the two graduation marks. Thus, the uncertain digit is calculated as (0.7 increment) * (1 °C/increment) = 0.7 °C. And, the temperature to be recorded is 87.7 °C.