In biochemistry, as in all other branches of chemistry, the reporting of data is, in many cases, as important as the experimentation, which took place to obtain the data. In our experience, in teaching the biochemistry laboratory course, we have found that many students feel that the strict adherence to reporting experimental data with the correct number of significant figures is a task only needed in the analytical chemistry laboratory. The lax attitude towards significant figures, scientific notation, accuracy and precision has caused much confusion for the students when reporting their experimental findings. Therefore, it is in the students’ best interest to review the following rules regarding the basic principles for reporting experimental findings:

Number of Significant Figures

In general, the number of significant figures pertains to the number of digits recorded for the value of a calculated or a measured sum. Ultimately, the number of significant figures is an indication of the precision of the measurement or calculation (precision will be discussed in statistics section).

If, for example, a student weighs the mass of a biological sample to be 0.998, 0.997, and 0.999 g for 3 separate measurements, a total of 3 significant figures would result from each of the measurements (zeros here are not significant). The fluctuation in the third decimal place indicates that this number is an estimate and is an indication of the balance limit. If a less accurate balance were used the measurements may look something like 1.0, 1.0, and 1.0 g. The measurements on the crude balance would result in each of the measurements having 2 significant figures (zeros here are significant). The aforementioned example illustrates the problem for most students, “which zeros are significant and which are not.” The rules for significant figures that follow should clarify any questions:

• 1. All digits are significant except zeros at the beginning of a number and possibly those at the end of a number (Rule 2 and 3 apply to terminal zeros).

• 2. All zeros, which terminate a number and are to the right of a decimal place are significant. For example, from our biological sample listed above, 1.0, 1.00, and 1.000 g. These examples contain 2, 3, and 4 significant figures respectfully.