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A unit is what a reading is expressed in: what the number is a number of. A count, a percent and a currency amount that print the same figure have said different things, so the unit is part of the calculation rather than a presentation choice. Each unit declares which arithmetic forms it fits, which is what lets a check refuse a rate measured in a count.

What you can do with a unit

• tableEvidence Plan · Settings

Its units— 7

• CountA number of things counted, each the same kind of thing: visits, leads, deliveries, people reached. It is the unity, coded 1, and it has no scale but the thing it counts, so two counts compare only when they count the same thing over the same period.
• PercentOne part in a hundred of a stated whole: a name for the number 0.01, and a quantity of dimension one. A reading in percent must say what whole it is a share of, because a share of visits and a share of visitors print the same and mean different things.
• RatioOne quantity over another, read as a multiple or as so many of one per one of the other: revenue over cost, deliveries over people reached. Where the two are in the same unit the ratio is of dimension one and reads as a multiple; where they differ the reading carries both units and says which.
• CurrencyAn amount of money in the currency the reading is published in, named by its ISO 4217 code. Money is not a physical quantity and the unit codes leave it out, so the currency and the date of its rate travel with a published reading; here the unit says only that the number is money, whether an amount, an amount per outcome, or a value on one relationship.
• RankAn ordinal position in a rendered order: first, second, later. An ordinal quantity has an order and no arithmetic, so ranks are compared and never added or averaged as if the gaps between them were equal.
• ScoreA composite standing on a stated scale, built from several readings judged against thresholds. It is a number by construction rather than by measurement, so it compares only with a score built the same way, and its movement reads only alongside what went into it.
• DurationA length of time: the seconds an impression must stay in view, the minutes after which a visit ends, the days a window reaches back. It is a quantity of time and names its unit of time, so two durations compare only when both name the same one.

Why it matters

What goes wrong without it, as the commitments that license this kind say it, each standing on its sources.

• A reading names its unit, and the unit fits its formA number without its unit is not a reading. Metrology defines a quantity value as a number and a reference together, and the unit codes exist because a value that travels without its unit is misread at the far end: a rate and a count that print the same figure have said different things, and percent is a name for the number 0.01, not a kind of thing. This model already fixed a KPI's direction and form as facts in the graph; the unit is the third fact of that family. Declaring which forms a unit fits is what a unit ontology does when it binds units to kinds of quantity, and it turns unit-form agreement from a review into a check.
  International Vocabulary of Metrology: Basic and General Concepts and Associated Terms (VIM), JCGM 200:2012 · ISO 80000-1:2022 Quantities and units, Part 1: General · The Unified Code for Units of Measure, version 2.2 · QUDT Ontologies: Quantities, Units, Dimensions and Data Types, release 2.1 · ISO 4217 Currency codes