Module fact 

A value that carries its measure, its provenance and its as-of.

A number on screen is a claim. Measured keeps the three things that make it honest together, so an app cannot render the number without also having the answer to “measured how?”, “from where?” and “when?”: a Measure naming what it counts and its unit, a source naming where the reading came from, and an as-of instant that makes it age on screen (stale past its own expected interval).

Unknown is a designed state, not zero: Measured::unknown carries the reason (and the action that would resolve it) and renders an em dash. A number is never a stand-in for “we did not measure”.

The type is what a view renders, not a widget: Measured::value_or_dash in the value position, Measured::caption under it (provenance is always the caption line, never beside the value), and Measured::is_stale dimming the provenance rather than the value.

use tilo_ui::fact::{Measure, Measured};
use tilo_ui::time::{Duration, UNIX_EPOCH};

let at = UNIX_EPOCH + Duration::from_secs(120);
let memory = Measured::known(
    Measure::new("Memory in use").unit("GiB"),
    "8.6",
    "this device",
    at,
    Some(Duration::from_secs(5)),
);
assert_eq!(memory.value_or_dash(), "8.6");
assert!(!memory.is_stale(at + Duration::from_secs(2)));

Structs

Measure

What a value counts, and the unit it counts in.

Measured

One value as the app knows it: a measurement with provenance, or the reason it has none.