QCS-016 - Quality Operations Procedures for Pharmaceutical, API, and Biotechnology - page 84

SOP No. QCS-016.00 Effective date: mm/dd/yyyy
Approved by:
16.3.3.2.1 Measurement
For a numerical quantity which is the result of a direct measurement, the number of decimal digits
in that quantity is generally fixed by the measuring device. The number of significant digits can
depend on the value of the measurement.
For experimentally determined quantities, the number of significant figures is not simply related
to the intrinsic precision of a device. Consider the buret and the analytical balance.
The buret permits a volume to be read to ±0.02 mL (one-fifth of the smallest division on its
scale). How many significant figures does such a quantity have?
If the volume is <1.00 mL, the number of significant figures in the volume is two (e.g., 0.57 mL).
If the recorded volume is between 1.00 and 9.99 mL, the number of significant digits is three. If the
volume is between 10.00 and 50.00 (the maximum capacity of the buret), the number of significant
figures in the volume reading is 4, the maximum number of significant digits that a 50 mL buret is
capable of producing.
Buret readings must always be reported to two decimal places, regardless of the volume reading.
The number of significant figures in the reading clearly depends on the magnitude of the reading.
Next, consider the analytical balance.
The analytical balance is capable of measuring weights to ±0.0001 g.
The number of significant figures represented by this intrinsic precision varies with the total
weight of an object. Nevertheless, weights determined on an analytical balance must always be
reported to four decimal places, regardless of the weight. Again, the number of significant figures
in the weight depends on the weight. For example,
For weights:
• <1 mg (0.0010 g), the balance produces only one signiicant igure (e.g., 0.0006 g = 0.6
mg).
• Between 1.0 and 9.9 mg (0.0099 g), the balance produces two signiicant igures (e.g.,
0.0066 g = 6.6 mg).
• Between 10.0 and 99.9 mg (0.0999 g), the balance produces three signiicant igures (e.g.,
0.0666 g = 66.6 mg).
• Between 100.0 and 999.9 mg (0.9999 g), the balance produces four signiicant igures (e.g.,
0.6666 g = 666.6 mg).
• Between 1.0000 and 9.9999 g, the balance produces ive signiicant igures (e.g., 6.6666 g).
• For weights between 10.0000 and 99.9999 g, the balance produces six signiicant igures
(e.g., 66.6666 g).
16.3.3.2.2 Computation
For a computed quantity, the number of significant digits reflects the number of digits in the num-
bers from which it is computed.
The number of significant figures in a computed quantity may be the same as or different from
those of the quantities from which it is computed. Consider a container that together with its con-
tents weighs 35.2749 g. A sample of the contents is transferred out, producing a final weight of
35.2235 g. Both the initial and final weights are known with a precision of six significant figures.
The weight of the sample is
35.2749 g
−35.2235 g
0.0514 g