# Difference between revisions of "Basics"

## Nomography

Nomography may be considered as a graphical computation. By using straight edge (or ruler) and pen, one can solve how parameters relate to each other.

Nomography was invented in the end of 19th century and it was workhorse in engineering up to 1960s. After that computers were more and more used for computations and nomography turned out to be forgotten state of art. Today we use spread-sheet calculators with computers and compute with them how parameters relate to each other. However, by using this approach, we have difficult to understand relations intuitively. It is also today very difficult to present graphically how more than three variables relate to each other. So we have almost lost a way to present laws (nomos) graphically (graphy).

Below are two examples of the use of nomography in order show how nomographs may be used in practice.

### Example 1

This is a classic nomography example. The question is about body-mass-index that is a measure of over- or underweight. The index is calculated from height and weight, and if it turs out to be between 20 and 25, person has normal weight.

In the example we have person with weight 85 kg and 183 cm. By drawing a straing line between the points in the scales, one can read that body-mass-index is some 25.5 so the person just crossed the limits of normal weight and has slight overweight. The red line for calculation is drawn in the nomograph below.

Body mass index Generated portable document file (pdf): File:Ex BMI.pdf

This example is one of the most simple examples illustrated in Examples. One may see how it was constructed with PyNomo in Body-mass_index.