Editing Omicron (section)

===Greek numerals===
{{main|Greek numerals}}
There were several systems for writing [[Greek numerals|numbers in Greek]]; the most common form used in late classical era used omicron (either upper or lower case) to represent the value 70.

More generally, the letter omicron is used to mark the fifteenth ordinal position in any Greek-alphabet marked list. So, for example, in [[Euclid]]'s [[Euclid's Elements|''Elements'']], when various points in a [[geometry|geometric]] diagram are marked with letters, it is effectively the same as marking them with numbers, each letter representing the number of its place in the standard alphabet.{{efn
|name=ordinal_greek_letters|
Greek [[Greek numerals|letters-as-numbers]] used an older Greek alphabet with three more otherwise unused letters, two of them re‑instated in their old locations, early in the alphabet. So positions higher than 5th place ({{mvar|[[ε]]}}) were shifted from the standard alphabet; 5th place was marked with normal fifth letter [[epsilon]] ({{math|[[ε]]}}). The 6th letter in the conventional alphabet, that normally follows  {{math|[[ε]]}}  is  {{math|[[ζ]]}}  ([[zeta]]) but the ''number'' 6 was represented a revived ancient letter {{mvar|{{prime}}[[ϝ]]}} ([[digamma]]), followed by {{math|{{prime}}[[ζ]]}} which was pushed up from 6th to its ancient position (7th) to represent the number 7. All of the letters after {{math|[[ζ]]}} were likewise shifted up one place, until the second ancient letter [[koppa (letter)|koppa]], ({{math|[[ϙ]]}}), was reached; it fell between {{math|[[Pi (letter)|π]]}} and {{math|[[ρ]]}}. Every letter from [[ρ]] to [[ω]] was shifted ''two'' places past its conventional ordinal position. Last place coming right after [[omega]] ({{math|[[ω]]}}, 800) was [[sampi]] ({{math|ϡ}}) which represented 900. (From that point, the system restarted, with a new tick-mark, at {{math|'''{{big|͵}}'''[[α]]}}. The tick-mark was put in a different place ({{math|'''{{big|͵}}'''[[α]]}} rather than {{math|{{prime}}[[α]]}}) to show that the letter represented a multiple of 1,000 rather than 1.){{Citation needed|date=July 2021}}
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|name=diagrams|
From [[Euclid's Elements|Euclid]] up to the 19th&nbsp;century, mathematical and technical diagrams were habitually marked sequentially with letters (or numbers),{{Citation needed|date=July 2021}} whereas in modern mathematical and scientific diagrams, it is much more common to choose for markers letters that might remind readers of the ''word'' used to describe the item in question.{{Citation needed|date=July 2021}} For example, [[Feynman diagram]]s in [[particle physics]] label the positions of particles with the first letter of their name, either in the Latin or Greek alphabet. So &nbsp;{{math|p}}, {{math|n}}, and {{math|e}}&nbsp;, represent the position on a diagram of a &nbsp;[[proton|<u>p</u>roton]], [[neutron|<u>n</u>eutron]], and [[electron|<u>e</u>lectron]],&nbsp; respectively. The [[neutrino|<u>n</u>eutrino]] is represented by {{mvar|[[ν]]}} (Greek [[ν|"nu"]]), since the Latin letter "{{math|n}}" is reserved for the [[neutron|<u>n</u>eutron]].{{Citation needed|date=July 2021}}
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