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Uncertainty in Measurement

April 15, 2013

Introduction to uncertainty in measurement

When a measurement is taken it can be approximate to the closest decimal point. There is always a scope for error in the measurement which leads to an uncertainity in the measurement.Uncertainty in measurement can be due to measuring instrument, the environment in which the measurement is taken, by the person taking measurement or the item that is measured.

Uncertainty in measurement

When we say that a stick is 6 feet long, we compare it with the measuring tape and the unit of measurement. In this case the unit is foot. We can state that the stick is 6 times one foot.  Thus we see that measurements are comparisons.

These comparisons involve uncertainties to some extent. If the object is between the 6th foot and 7th foot, one has to take the closest mark on the tape to state the measurement. Note the following example, a beetle is measured in the example.

Uncertainty in beetle measurement 1

length of a beetle

What is the length of the beetle in the picture? Between 0 and 2 in
Between 1 and 2 in
Between 1.5 and 1.6 in
Between 1.54 and 1.56 in
Between 1.546 and 1.547 in

The length of the beetle can be stated as 1.546+ or 1.547-

Ways to avoid unceratinities in measurement

Some of These uncertainties can be avoided by carefully calibrating the measuring scale, by noting down the measurements correctly, and or by cross verifying. The uncertainties in measurement can be estimated using statistical methods.  To know the uncertainty, we need to first determine the error.

Error is the different between the actual correct measurement and the measurement taken. If we know the scope for error in a particular instrument, we can use the uncertainty quotient and correct the measurement to a great extent. Suppose in the above example, the uncertainty quotient is + or – 0.05. Then when we measure the beetle we can say that the beetle is 1.5 ±.05

Conclusion for unceratinities in measurement

Uncertainty exists in all types of measurement at some level. These can be corrected to some extent by taking due care. The measurements are usually accompanied by a statement that explains the uncertainties in the measurement and also states what the measuring instrument is fit for.  By knowing this we can use the right kind of measuring instrument for the job.


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