By definition: ruler is a 'tool with straight edges, with the objective of drawing straight lines' and, in the metrology, scale is the 'set of marks, associated to any numbering, that makes part of one device with display of one measurement instrument'. By use and tradition, it is common in the metal mechanic offices to refer to the line gauges as scales. In some moments, this page will follow that culture.
The geometry simple and efficient of the scales allows to find this kind of instrument in many different professional enviroments, for example: in the metal mechanic offices, engeneeiring, in the work desks of many professionals, in the technical draw classes, geometry, maths among others. The utilization of the concept of 'line gauge' is also found with variations, for example: the named 'carpenter meter tool' animation 1 - that is one rigid ruler relatively long - two meters, for example - graduated, segmented and articulated that can be folded until fit in a toolbox or drawer; a measuring tape that is a strip of steel with scale graved in ink in one of it faces that can curl in a pulley and retract in a little box that fits in your pocket, for example; a 'measuring tape' instrument of measurement of the tailors and dressmakers, the graduation applied in a fabric tape; and so on. The scales can be found in steel stainless, wood, plastic, fabric, and sometimes the graduation is graved from the right to the left, in a non ending of variations.
animation 1 - use of carpenter meter
The ruler represented on this simulator is 1:100. This means that the numbering graved in the ruler represents the hundredth part of the meter, or centimeter. The centimeter is subdivided by ten, this means that exah mark of the instrument of measurement represents to one millimeter that is the thousandth part of the meter.
figure 1 - one use of the scale
The scale (instrument) of this simulator is specific for measurement, because, differently of the ruler used in the drawing classes, the mark of the zero coincides with the top, allowing to measure rebounds or heights with relativilly precision - figure 1. This engeeniering of the layout bring to us a problem. With the continuos use during the years, the point of the scale wears out and the measures start to be with less precision. Because of that it is recommendable that we use some mark, for example: in the figure 2 the mark used as zero was of the ten millimeters and them we subtracted this value from the measured one, to obtain the real measure: 62mm - 10mm = 52mm.
figure 2- measure with one scale (measurement instrument) or line gauge
Observe in the simulator that is not possible to be sure how much the border of the mensuring is between the marks. this simulator indicates this fact imputing one number five between parenthesis (5). technological devices as the vernier correct this limitation.
Observe also that it is not possible to be sure when the mark is aligned with the border of the mensuring in both sides. This lack of precision of reading has as consequence that the measure taken is less trustful or not precise. Instruments as the vernier caliper corrects this limitation.