Notation and Datum

noun

• A technical system of symbols used to represent special things.
  • synonyms: notational system
• A comment or instruction (usually added. )
  • usage: "his notes were appended at the end of the article"; "he added a short notation to the address on the envelope"
  • synonyms: note, annotation
• The activity of representing something by a special system of marks or characters. .

• (n.) Literal or etymological signification.
• (n.) Any particular system of characters, symbols or abbreviated expressions used in art or science, to express briefly technical facts, quantities, etc. especially, the system of figures, letters, and signs used in arithmetic and algebra to express number, quantity or operations.
• (n.) The act or practice of recording anything by marks, figures or characters.
• (n.) The act or practice of recording anything by marks, figures or characters.
• (n.) Any particular system of characters, symbols or abbreviated expressions used in art or science, to express briefly technical facts, quantities, etc. especially, the system of figures, letters, and signs used in arithmetic and algebra to express number, quantity or operations.
• (n.) Literal or etymological signification.

noun

• An item of factual information derived from measurement or research.
  • synonyms: data point

• (n.) Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based; -- used chiefly in the plural.
• (n.) The quantities or relations which are assumed to be given in any problem.

(DoD, NATO) Any numerical or geometrical quantity or set of such quantities which may serve as reference or base for other quantities. Where the concept is geometric, the plural form is "datums" in contrast to the normal plural "data."

datum is a horizontal plane from which heights and depths are measured.