Biomedical Engineering Reference
In-Depth Information
Fig. 8.2
Measurement of
the length of an object with
a ruler with the smallest
division in millimeters
1
23456
7
cm
and the fifth readouts are incorrect due to the lack of a digit in the first case and to
the excess of digits, in the second case. If the length of the object is between 4.0 and
4.1 cm, the measurement should be written 4.00 or 4.04 or 4.08 cm, for example,
with all significant digits. Observe the importance in using apparatus with great
precision, but it is still more important to write correctly the performed readouts.
Very expensive, precise equipment is valueless if the experimenter does not know
such rules.
We should remember that the digit zero is only significant if it is located to the
right of a significant digit. Then,
0.00030 has only two significant digits, which are 3 and 0
350,000 has six significant digits
8.2.2 Mathematical Operations with Significant
Digits: Two Examples
Sum
34.4
0.006
115
149.406
The correct form to write the result of sum is 149, since the unit is a doubtful
digit because it has been estimated. It is purposeless to write decimal digits in the
result, due to the number 115. The result was rounded off to three significant digits.
Multiplication
3.14
1.0
3.1
In this case, the result of multiplication cannot have more significant digits than
the quantity of digits in the least significant digit used in the calculation (1.0).
