A custom mark type that turns one measure + one date into a clean, interactive metric card, bound to the Marks card (so it travels with the worksheet).
Shared viz-extension techniques (reading encodings, live updates, responsive/no-scroll degradation, etc.) live globally in
reference/viz-extensions.md. This file covers only what's specific to the Metric Card.
#What it is
- Headline value (BAN) + a ▲/▼ delta chip and a comparison line.
- Headline value: the total of the range (default; brushing a window totals that window), or the latest period. Hovering a bar always reads that period.
- Comparison resolves by the mode you pick:
- Period over period (default), with a total headline, the window vs the equal-length window before it (the full range, with nothing before it, shows the latest period's change on the comparison line); with a latest headline, the latest period vs the one before it. No setup.
- Prior period (parameters), split the bound rows by two workbook date
parameters (
Prior Period Start/Prior Period End): rows in that range are the reference, rows after it are the current window. One parameter pair works for every card on the dashboard. - Prior period (flag field), a boolean field on the Prior flag shelf marks each row prior (TRUE) or current. The prior rows become the reference.
- None, value + chart only.
- Trend chart: median-graded bars (bars on the "good" side of the median read bold, the other side fades, so notable periods pop without a hover) or a line/area. Hide it entirely for a big-number tile.
- Play / replay / compare buttons (top right; Configure can hide them): play draws the chart in while the headline counts up; compare overlays the previous period (the prior-period split, the window before a brush, or the latest half vs the half before) with both totals.
- Value ↔ chart balance slider grows the number and shrinks the chart (or the reverse) without changing the tile size.
- Number format: number, currency, percent (with a 0–1 ratio option), or
duration (a seconds value as
HH:MM:SS), applied to the headline, chart labels, and tooltips. Optional compactK/M/Babbreviation. - Aggregation: auto (read from the field name), sum, average, min, max, median.
- Direction: mark whether up or down is "good", colors the delta accordingly.
- Scrub a point to read it; brush a date window (drag) to select those marks and filter the dashboard; click / double-click resets.
- Light / dark theme, size scale, a user-pickable accent, and it sheds detail near the size limits down to number-only.
- Configure (the ⚙ gear, top-right) live-previews every change on the card as you make it; Save persists to the workbook.
#Encodings (Marks card)
| Tile | Required | Accepts |
|---|---|---|
| Measure | yes | one continuous measure (e.g. SUM(Sales)), the headline + chart value |
| Date | yes | one date, use a continuous date (e.g. MONTH(Order Date)) |
| Prior flag shelf | no | a boolean field, TRUE for prior-period rows, only for the "prior period (flag field)" comparison mode |
#Run it locally
From the repo root: python scripts/kitserve.py (serves every extension on 8765).
It answers on both IPv4 and IPv6 and resolves lib/ to _shared/lib; a plain
python -m http.server does neither, which is what makes a local extension load
as a blank or errored zone.
In Tableau, on a worksheet's Marks card → mark-type dropdown → Add Extension… → Access Local
Extensions → manifest.local.trex. Drag a measure onto Measure and a
continuous date onto Date.