What's the difference between ruler and straightedge?

Ruler

Definition:

(n.) One who rules; one who exercises sway or authority; a governor.
(n.) A straight or curved strip of wood, metal, etc., with a smooth edge, used for guiding a pen or pencil in drawing lines. Cf. Rule, n., 7 (a).

Example Sentences:

(1) In his notorious 1835 Minute on Education , Lord Macaulay articulated the classic reason for teaching English, but only to a small minority of Indians: “We must do our best to form a class who may be interpreters between us and the millions whom we govern; a class of persons, Indians in blood and colour, but English in taste, in opinions, in morals and in intellect.” The language was taught to a few to serve as intermediaries between the rulers and the ruled.
(2) After violence had run its bloody course, the country’s rulers conceded it had been a catastrophe that had brought nothing but “grave disorder, damage and retrogression”.
(3) A modification of a previously described curved ruler, the current model has a hinge for greater ease of maneuverability and a "T" piece on one end to facilitate measurement and marking of both poles of the muscle without repositioning the ruler.
(4) Fail, and the nation’s rulers face embarrassment in front of a television audience of more than a billion.
(5) The former military ruler won the key prize of Lagos, Nigeria’s commercial capital, but at one point his lead was cut to 500,000 votes after landslide victories for Jonathan in his southern Delta homeland.
(6) The ruler is especially helpful when one is doing large recessions and posterior fixation of the recti muscles (Faden operation).
(7) While Egypt's military rulers were quick to blame football hooliganism, a group of hardline Al Ahly fans, known as ultras, accused the police of intentionally letting rivals attack them because of their historic antipathy to the security forces and their role at the forefront of anti-Mubarak protests a year ago.
(8) What was it that so alarmed Brazil's military rulers, and why, 40 years on, does Tropicália still inspire as well as provoke?
(9) Throughout ancient Egyptian history, rulers changed capitals to enforce a sense of national renewal or unity – a trend that began with the first purpose-built capital of a united Egypt , some 5,000 years ago.
(10) This civilisation was later cross-fertilised by new influences brought by the Kushans who succeeded the Bactrian Greeks as rulers of Afghanistan, while adopting much of their culture.
(11) But the SNP has plenty to learn from the home rulers at Westminster.
(12) The one thing romantics have to remember is that though you might well try to stop your daughter getting mixed up with one, there is no necessary connection between being a good ruler and being a loving and faithful mate.
(13) Using the technique and the ruler described by Schei et al., the radiographic height of the alveolar crest from the cemento-enamel junction was determined.
(14) Quantitative analysis of the density data is consistent with the presence of up to six strands of a protein molecule in the central channel that could serve as the template or ruler structure that determines the length of the bacteriophage tail and that could be injected into the cell with the phage DNA.
(15) Meles Zenawi , the cerebral ruler of Ethiopia for the last 21 years, is a man with many reputations.
(16) In that same 2010 fundraiser speech, Perry described his mission as "bigger than any law or policy," of being engaged in a struggle not of "flesh and blood," but "against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms".
(17) Abdul Halim, who was installed as ruler of his state in 1958, has been described by his family as a caring leader and a fan of Frank Sinatra, Dean Martin and Nat King Cole.
(18) A poor citizen can’t even find one kilogramme of rice on the street,” he said, arguing that the country’s rulers would face divine judgment for what they were doing to the poor.
(19) Diplomatic tensions also intensified with Bahrain recalling its ambassador to Tehran, following the Iranian foreign minister Ali Akbar's warning on Monday that Bahrain's rulers and the Gulf states who have sent troops to the kingdom needed to act with "wisdom and caution".
(20) Mugabe’s officials have repeatedly accused the US of seeking regime change, a common charge levelled by rulers across the continent.

Straightedge

Definition:

(n.) A board, or piece of wood or metal, having one edge perfectly straight, -- used to ascertain whether a line is straight or a surface even, and for drawing straight lines.

Example Sentences: