Scales

An engineer's scale is a tool for measuring distances and transferring measurements at a fixed ratio of length. It is commonly made of plastic and is just over twelve inches (300 mm) long, so that the measuring ticks at the edges do not become unusable by wear. It is used in making engineering drawings, commonly called blueprints, in scale. In scientific and engineering terminology, a device to measure linear distance and create proportional linear measurements is called a scale. A device for drawing straight lines is a ruler. In common usage both are referred to as a ruler.

In Canada and the United States, this scale is divided into decimalized fractions of an inch, but has a cross-section like an equilateral triangle, which enables the scale to have six edges indexed for measurement. One edge is divided into tenths of an inch, and the subsequent ones are directly marked for twentieths, thirtieths, fortieths, fiftieths, and finally sixtieths of an inch. The engineer's scale came into existence when machining parts required a greater precision than the usual, binary fractionalization of the inch as in the architect's scale for houses and furniture. They were used, for example, in laying out printed circuit boards with the spacing of leads from integrated circuit chips as one-tenth of an inch. In the twenty-first century, those which are commonly purchased in the US are actually made in Germany.

An architect's scale is a specialized ruler. It is used in making or measuring from reduced scale drawings, such as blueprints and floor plans. It is marked with a range of calibrated scales (ratios). For accuracy and longevity the material used should be dimensionally stable and durable. Scales were traditionally made of wood, but today they are usually made of rigid plastic or aluminum.

The definition or specification of precise standards of measurement involves two key features, which are evident in the International System of Units (SI). Specifically, in this system the definition of each of the base units refer to specific empirical conditions and, with the exception of the kilogram, also to other quantitative attributes. Each derived SI unit is defined purely in terms of a relationship involving it and other units; for example, the unit of velocity is 1 m/s. Because derived units refer to base units, the specification of empirical conditions is an implied component of the definition of all units.