Gauge

Gauge shows a reading between Minimum and Maximum as an arc — a CPU load in a status panel, a frame budget in an overlay, a tank on a HUD.

Doc 49 § 7.1 ranks "Gauge / LevelIndicator" sixth of the controls this set was missing. It is the level indicator drawn round a circle, and deliberately nothing more. A bar suits a reading that sits in a row beside the word for what it measures; a dial suits one that sits on its own — the corner of an overlay, the middle of a card. What the reading means is the same, so the two share everything that decides it: a capacity rather than a job, announced as ARIA's meter with the reading as its value.

Warning, Critical, Direction and Level are the level indicator's, computed by the same code — a bar and a dial over one number cannot disagree about whether it is a problem. In short: with two lines their order is the direction, with one line Direction says which way is worse, and an unset line (float.NaN) never fires. The level indicator page has the reasoning, including why a lone line with no stated direction reads upward.

The level reaches the stylesheet as the same two classes, and ControlTheme.vcss colours them the same way:

⚠ The dial opens at the bottom and fills clockwise from its lower left, which is what a speedometer, a pressure gauge and every audio meter with a needle does. Sweep is how much of a whole turn it spans: three quarters by default, held between a tenth and one. A sweep of one is a closed ring whose ends meet at the bottom.

The arc's width is the theme's, as --arc-width — five pixels on the default 48-pixel dial:

The dial is drawn in the largest square that fits the element and centred in it. Orientation, which every range control inherits, means nothing to a dial and is ignored.

A frame budget beside a memory pool, and a fuel tank with a single line:

Samples/02-HelloUi's gallery puts one beside the level indicators in its Feedback card, driven past both of its lines by the same clock.

• No needle. The filled arc's end is the needle; a separate one is another shape to antialias at every angle and says nothing the arc does not.
• No text in the middle. "87 %" is not a sentence this assembly can write without knowing what is being measured — the level indicator's rule. Put a label over it.
• Square ends. A round cap reaches past the reading by half the arc's width, so an empty gauge would still show a dot.
• Not focusable. It is a readout, announced as ARIA's meter with the reading itself as its value.

• Level indicator — the same reading as a bar, and where the threshold rules are explained.
• Accessibility — why a capacity is a meter and not a progressbar.