The foldable meter is a length measuring instrument consisting of a group of rulers hinged to the ends, normally folded together for convenience, which, when re-aligned and loosened, produce a single rod metric of discrete dimensions.

This tool is already built in antiquity to provide tools for measuring lengths of a certain size, without having to carry long metric rods. An example can be seen in the Egyptian Museum of Turin, where there is a folding cubit belonging to the funeral kit of Ka architect. Still today, for its practicality, it is used in building and carpentry.

Traditionally, foldable meters are made of wood, in which the staircase is realized by engraving the material and painting black marks and numeric indications. This preserves the scale reading even when the instrument is ruined or worn. Even today, wood tools are very common, although recently they tend to replace them with economic versions made of rigid plastic molded. Metal versions are unusual due to excessive weight, though rarely made in aluminum.

Single rulers are usually 20 cm so that the instrument can be put into the pocket when folded (but they have a base size of 10 cm to 50 cm); while chains composed of 5-10 pieces are normally hinged. The overall size is therefore 2m, with the possibility to find folding meters of 1-5m.

In the past, maintaining the alignment of the various rulers was left to the expertise of the user and the clutch present in the hinges, today, at the hinges, trapezoidal engravings are realized which, on the one hand, reduce the accidental closure of the meter, on the other hand, align the rulers with the rulers.

Normally these instruments have two scales on opposite sides, one from one end to the other. The beginning of the scale coincides with the ends of the two rulers that make the terminal of the chain; this to make it possible to read depth or length by batting with the surface. For this, it is common that these ends are protected with metal plates.

The typical resolution of these scales is millimeter.

Despite all the structural changes, these meters for stiffness limits, building defects, deformation and decay tendencies during use are not intended for precision measurements. Normally one can expect measurements of uncertainty of some millimeter order. Voices correlateemodify wikitesto Other designers wikitesto

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