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1:20 and 1:40 scales are used for working plans. 1:60 is normally used only to show large areas of a project. In 1918 French described the US engineer's scale using the term "civil engineers' scale", and it was said to be "used for plotting and map drawing, and the graphic solution of problems." [3]
Area; system unit code (alternative) QID symbol or abbrev. notes sample default conversion combinations SI: square kilometre: km2 Q712226: km 2: US spelling: square kilometer: 1.0 km 2 (0.39 sq mi) km2 sqmi; square hectometre: hm2 Q35852: hm 2: US spelling: square hectometer: 1.0 hm 2 (2.5 acres) square decametre: dam2 Q23931040: dam 2: US ...
The quectometre (SI symbol: qm) is a unit of length in the metric system equal to 10 −30 metres. To help compare different orders of magnitude , this section lists lengths shorter than 10 −30 m (1 qm).
The value of π as used by the Greek mathematician and scientist Ptolemy was 3;8,30 = 3 + 8 / 60 + 30 / 60 2 = 377 / 120 ≈ 3.141 666.... [28] Jamshīd al-Kāshī , a 15th-century Persian mathematician, calculated 2 π as a sexagesimal expression to its correct value when rounded to nine subdigits (thus to 1 / 60 9 ...
Other uncommon metric units of area include the tetrad, the hectad, and the myriad. The acre is also commonly used to measure land areas, where 1 acre = 4,840 square yards = 43,560 square feet. An acre is approximately 40% of a hectare. On the atomic scale, area is measured in units of barns, such that: [13] 1 barn = 10 −28 square meters.
10 −30: 1 square femtometre (fm 2) 1 fm 2 10 −29 66.52 fm 2: Thomson cross-section of the electron [4] 10 −28 100 fm 2: 1 barn, roughly the cross-sectional area of a uranium nucleus [5] 10 −24: 1 square picometre (pm 2) 1 pm 2 10 −20: 1 square angstrom (Å 2) 10,000 pm 2 10 −19: 100,000 pm 2: Area of a lipid bilayer, per molecule [6 ...
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A graphical or bar scale. A map would also usually give its scale numerically ("1:50,000", for instance, means that one cm on the map represents 50,000cm of real space, which is 500 meters) A bar scale with the nominal scale expressed as "1:600 000", meaning 1 cm on the map corresponds to 600,000 cm=6 km on the ground.