# Science and Common sense

by Nikolai V. Shokhirev

## Measurements

### Contents

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Previous (Science is measurement. Great Discovery. How to make the right angle. From Alchemy to Chemistry. Science is purified and extended measurement)
Everyday measurements, Direct and indirect measurements,  Incomplete measurements,  How to fool customers, How to handle indirect measurements
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(Examples: Measurement of Skin Smoothness, Safe Distance Measurements)

### Everyday measurements

In our everyday life we usually use very simple measurement tools (like rulers, watches, etc.). But most extensively, we use our "built-in" tools: eyes, ears, nose, tongue, hands. All properties summarized in the previous section can be applied to these tools as well. The most important features we should know about our tools are:

• Accuracy (errors of measurements)
• Resolution (smallest distinguishable difference)
• Intervals of reliable measurements

Some examples are discussed below:

### Direct and indirect measurements

If some unit of measure can be applied directly, then this type of measurement is called a direct measurement. Consider the following example:

The other type of measurement is indirect measurement. Consider the following:

Human eyes determine the distance from the different angles of the each eye line of sight:

The determination of the distance L requires additional processing:

In this case this is done in our brain.

In other words, for indirect measurements we measure what we can (length in the example below) in order to figure out  what we want to measure (height):

In addition, the indirect measurements have processing error. More advanced discussion about indirect measurements can be found here (a part of my ABC tutorials).

### Incomplete measurements

Indirect measurements, not only have additional processing error, but they are also usually incomplete. This means, that not all parameters of the object that is being measured can be obtained. For example, laser atmospheric probing can detect only the particle within some region of a particular size and cannot see the other particles outside this region. It is necessary to use several types of measurements in order to collect the complete information.

Our main source of information are our eyes. This tool performs indirect measurements, detecting the light reflected from objects. The light excites retina cells and they generate nerve signals. Our brain processes the signals and creates images.

The processing is not perfect. Optical illusions are an example that demonstrates this.

 Is the left circle bigger? Count  the black dots! How many legs does this elephant have? Are the horizontal lines parallel or do they slope?

The processing cannot be perfect because the brain tries to reconstruct the three-dimensional world from the two-dimensional retina signals. The above optical illusions are a double-trickery because the initial image is also two-dimensional.

### How to fool customers (using indirect measurements)

It is easy to take advantage of  imperfect processing. The incompleteness of indirect measurements can be used to fool the customers. This is an example:

 Outsideview Optimisticprocessing Actualcross-section

However, in this case the direct measurement is available: read the label

You can find many other examples. Remember about the indirect measurements and do not let yourself be fooled.

### How to handle indirect and incomplete measurements?

Answer: Use the scientific approach. It should not be an exact science, just try to use creatively the solution from the previous section:

• Develop internal standards
• Try to estimate the errors
• Use tools with different measurement intervals
• Use complementary measurements
• Pay attention to the indirect measurements

In the next section we discuss some more examples.

More about measurements: Metric and Measure.

Up (Popular science)
Previous (Science is measurement. Great Discovery. How to make the right angle. From Alchemy to Chemistry. Science is purified and extended measurement)
Everyday measurements, Direct and indirect measurements, Incomplete measurements, How to fool customers, How to handle indirect measurements
Next
(Examples: Measurement of Skin Smoothness, Safe Distance Measurements)

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