# Rulers

This article is about the drawing and measuring instrument. Ruler can also refer to a statesman in charge or ceremonial head of state of a country or minor politically significant principality; for this meaning see Monarch or Lists of incumbents.

A variety of rulers
Retractable flexible rule
A ruler or rule is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is the instrument used to rule lines and the calibrated instrument used for determining measurement is called a measure. However, common usage is that a ruler is calibrated so that it can measure.

Several different designs of flexible instruments are used to determine length, such as the carpenter's rule, the ribbon-like tape measure used by tailors, and the retractable rule used especially in the construction trades and by home handyman, also known as a tape measure. As can be seen by the photos on this page, a 2 metre carpenter's rule can be folded down to a length of only 20 centimetres to easily fit in a pocket, and the 5 metre long tape easily retracts to fit within a small-sized housing.

Practical rulers have distance markings along their edges.
• The ruler (calibrated, though numbers are not shown) appears as a charge in heraldry, notably in the arms of Odouze.

## Ruler Applications in Geometry

''Main article: Compass and straightedge
In geometry, a ruler usually refers to an unmarked ruler, only used for drawing straight lines between points, not measuring. A ruler and compass construction thus refers to constructions using such unmarked ruler and a compass. It is known for instance, that the angle trisection problem is an impossible one, within the classic restriction of ruler bearing no marks. However, should a single mark be allowed on the ruler, the problem becomes solvable. It is common to call rulers in the geometric context as straightedges.

monarch (see sovereignty) is a type of ruler or head of state. Monarchs almost always inherit their titles and are rulers for life; that is, they have no term limit. Historically monarchs have been more or less absolute rulers.
lists of incumbents, i.e. lists of people in various offices and positions, including heads of states or of subnational entities.

A historical discipline, archontology, focuses on the study of past and current incumbents.
Measuring instruments are the means by which this translation is made. All measuring instruments are subject to varying degrees of instrument error.

Physicists use a vast range of instruments to perform their measurements.
Geometry (Greek γεωμετρία; geo = earth, metria = measure) is a part of mathematics concerned with questions of size, shape, and relative position of figures and with properties of space. Geometry is one of the oldest sciences.
Technical drawing, also known as drafting, is the practice of creating accurate representations of objects for technical, architectural and engineering needs. A practitioner of the craft is known as a draftsman, draftsperson
tape measure or measuring tape is a ribbon of cloth, plastic, or metal with linear-measure markings, often in both imperial and metric units. Surveyors use tape measures in lengths on the order of hectometres. It is a convenient, common measuring tool.
1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
1 centimetre =
SI units
010−3 m 0 mm
US customary / Imperial units
010−3 ft 0 in
A centimetre (American spelling: centimeter, symbol cm
In heraldry and vexillology, a charge is an image occupying the field on an escutcheon (or shield). Charge can also be a verb; for example, if an escutcheon bears three lions, then it is said to be charged with three lions.
Heraldry in its most general sense encompasses all matters relating to the duties and responsibilities of officers of arms.[1] To most, though, heraldry is the practice of designing, displaying, describing, and recording coats of arms and badges.
Compass-and-straightedge or ruler-and-compass construction is the construction of lengths or angles using only an idealized ruler and compass.

The ruler to be used is assumed to be infinite in length, has no markings on it and only one edge, and is known as a
Compass-and-straightedge or ruler-and-compass construction is the construction of lengths or angles using only an idealized ruler and compass.

The ruler to be used is assumed to be infinite in length, has no markings on it and only one edge, and is known as a
trisecting the angle is a classic problem of compass and straightedge constructions. Two tools are allowed:
1. An un-marked straightedge, and
2. a compass,

Problem: construct an angle one-third a given arbitrary angle.
For the subculture, see Straight edge.

A straightedge is a tool similar to a ruler, but without markings.

## Compass-and-straightedge construction

Main article: Compass and straightedge

Johannes Anton Ullrich (1826 - 1895) was a German industrialist, inventor, and co-founder of the "Gebrüder Ullrich" in the Rhineland-Palatinate.

## Life

Franz Ullrich was born on the 30 August 1826 in the small town of Maikammer, Germany.
Golomb ruler, named for Solomon W. Golomb, is a set of marks at integer positions along an imaginary ruler such that no two pairs of marks are the same distance apart. The number of marks on the ruler is its order, and the largest distance between two of its marks is its
A Measuring rod is a kind of ruler. This phrase is often used without mention of a particular kind or length of ruler and has been used since ancient times.

Greek κανων bar, measuring rod, ruler

• Levelling rod

A perfect ruler of length is a ruler with a subset of the integer markings that appear on a regular ruler. The defining criterion of this subset is that there exists an such that any positive integer can be expressed uniquely as a difference for some .
Rulering is the practice of using a ruler as a convenient, hence in some mainly scholarly traditions popular, tool for a corporal punishment, usually on the hands (either outstretched palms or knuckles) or thighs, although sometimes as a spanking (on the buttocks).
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).
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 300 mm (twelve inches) long, so that the measuring ticks at the edges do not become unusable by wear.
slide rule (often nicknamed a "slipstick"[1]) is a mechanical analog computer, consisting of at least two finely divided scales (rules), most often a fixed outer pair and a movable inner one, with a sliding window called the cursor.
tape measure or measuring tape is a ribbon of cloth, plastic, or metal with linear-measure markings, often in both imperial and metric units. Surveyors use tape measures in lengths on the order of hectometres. It is a convenient, common measuring tool.
vernier scale lets one read more precisely from an evenly divided straight or circular measurement scale. It is fitted with a sliding secondary scale that is used to indicate where the measurement lies when it is in-between two of the marks on the main scale.
A geometry template is a piece of clear plastic with cut-out shapes for use in mathematics and other subjects in primary school through secondary school. It functions as a stencil, protractor, ruler, and straightedge.
caliper (British spelling also calliper) is a device used to measure the distance between two symmetrically opposing sides. A caliper can be as simple as a compass with inward or outward-facing points.
A dividing engine is a device specifically employed to mark graduations on measurement instruments.

## History

There has always been a need for accurate measuring instruments.