Set Unit

Shipping

set_unit

Attach or relabel a quantity's unit without rescaling the numbers

Signature

Inputs

valueScalar|Signalrequired— The quantity whose numbers are kept and whose unit label is replaced.

Outputs

resultScalar|Signal— Same numbers and same σ² as the input, carrying the new (canonicalised) unit symbol.

Parameters

Key	Type	Default	Notes
`unit`	unit		Unit label to attach — the numbers are NOT rescaled (use Unit Convert for that). Typical use: annotate raw acquisition data. Empty strips the unit; unknown symbols auto-register as custom units. A syntactically invalid expression (`kg//m`) errors.

Description

Set Unit relabels a quantity's unit without touching its numbers — the semantic partner of unit_convert. Where convert preserves the physical quantity and changes the value, Set Unit preserves the value and changes what it means.

This is how raw, dimensionless data — an ADC stream, a CSV column, a formula result — is told "you are volts." The dimensionless-wildcard rule (ADR-006) makes that annotation legal everywhere downstream, so a bare number can be given a physical identity and then flow into unit-aware math.

The uncertainty passes through untouched: relabeling can't change the spread, so $σ^{2}$ is carried verbatim, and the σ-correlation lineage rides through unchanged (the operation is numerically the identity).

The unit expression is resolved leniently: unknown symbols auto-register as custom base dimensions (Apples is a feature, ADR-003), so you are free to invent domain units. The canonical resolved symbol is stored, so a u-spelled micro becomes µ, etc. A syntactically invalid expression (kg//m) is still an error. An empty expression resolves to dimensionless — i.e. it strips the unit.

Mathematics

v a l u e^{'} = v a l u e, σ^{'2} = σ^{2} (numbers untouched; only the label changes)

Examples

Annotate a raw ADC stream

A dimensionless signal [1.5, -2.5] (with $σ^{2} = [0.01, 0.04]$ ) fed through Set Unit with unit = V becomes the same samples [1.5, -2.5], same variances, now labelled $V$ . No value changed.

Strip a unit

A scalar $7 V$ with unit = (empty) becomes the dimensionless scalar $7$ . Useful before feeding a value into a context that expects a bare number.

Custom domain unit

A count of $3$ with unit = Apples yields $3 Apples$ ; the symbol auto-registers as a custom base dimension and propagates through downstream unit algebra.

Applications

Labelling raw acquisition data (ADC counts, CSV columns) with its true physical unit so downstream nodes carry correct dimensions.
Correcting or overriding a mislabelled unit without disturbing the recorded values.
Stripping a unit to obtain a bare number for a node or export that expects dimensionless input.
Introducing custom domain units (Apples, Widgets, packets) for non-SI bookkeeping that still benefits from dimensional tracking.

Neat

Set Unit and Unit Convert are exact mirror images: convert keeps the physical quantity and changes the numbers; Set Unit keeps the numbers and changes their meaning.

Because the resolver canonicalises symbols, sloppy input like `u` for micro or an alternate spelling normalises to the stored canonical symbol (µ) — the annotation is cleaned up as it is applied.

Unknown symbols are a feature, not an error: they auto-register as custom base dimensions (ADR-003), so inventing a project-specific unit just works.

Known issues

Set Unit never rescales — attaching `mV` to a signal that is really volts will mislabel it by a factor of 1000. Use Unit Convert when the numbers must change.

A syntactically invalid unit expression (e.g. `kg//m`) errors rather than being coerced.