Plumbline — identity sheet

Three icon concepts, the iteration passes on the winner, the six-variant suite, and the size tests. Nothing here is generated: every path is hand-set on a 48-unit grid.

Pass 1 — three concepts

Concept A

Plumb bob & datum

The instrument the theme is named for. Symmetric, vertical, obviously an object rather than a swoosh. Risk: the bob alone is a map pin.
Concept B

The column, one out of line

A vertebral stack with one segment displaced, and the datum that shows it. Says musculoskeletal instantly. Risk: chiropractic cliché, and the dashed rule dies below about 32px.
Concept C

Goniometer arc

The actual instrument used to measure range of motion. Trade-specific and owned by nobody. Risk: reads as a generic "growth/angle" mark, and it is not symmetric.

Pass 1 at 24px — the only test that matters

A
B
C

Read: B disappears — at 24px the dashed datum drops out and five stacked bars read as a hamburger menu. C reads as a tick, and it is the only asymmetric option in a sector whose marks are almost always symmetric about a vertical axis. A wins, but the pass-1 draft is too light: the crossbar and line make a thin “T” and the bob is a small teardrop — which is to say, a map pin.

Pass 2 — mass, and stopping it being a map pin

A · pass 2a

More mass, same teardrop

Heavier, but still a teardrop — still a pin with a stick on top.
A · pass 2b

Turned brass: shoulder, then straight cone

A real plumb bob is a turned object: rounded shoulder, then a straight conical taper to a machined point. The straight sides are the whole difference — a pin has none.
A · pass 2c

2b, with the datum in accent

The bar is the fixed reference, the bob is what moves against it. Giving the two different jobs different colours is the only reason for a second colour to exist.

Pass 3 — optical corrections on 2c

A · pass 3a

Narrower bar, longer drop

Bar pulled in so it is narrower than the bob's shoulder — the silhouette now steps out, not in. Tip overshoots to y45.5 because a point reads short against a flat-bottomed neighbour.
A · pass 3b

3a + suspension notch

A second accent mark at the widest point. Adds the “measured” reading but it is the first thing to fail at small sizes — see the size row.
A · pass 3c — FINAL

3a, bar squared

Square ends on the datum bar. A rounded bar reads soft and optical — this bar is a fixed reference, so it gets machined ends, and it holds its length at 24px where a rounded one loses 3 units to the caps.

Iteration at 24px

1
2b
3b
3c

The wordmark — constructed, not set

Drawn on the same 48-unit grid as the mark: monoline, stroke 3, cap height 24, round joins, one letter box per glyph. It is not the display face — a theme logo ships as a data URL and cannot load Epilogue, so a wordmark that depends on a webfont renders as Arial in the editor. Constructing it also matches what the mark is: a drafted instrument.

Draft: round caps, metric spacing. Terminals read soft against a machined mark, and P→L is loose while L→U is tight.
Final: butt caps, round joins — machined ends, soft corners, which is the theme's dial pair stated in the letterforms. Sidebearings retuned optically: L→I is the tightest pair, I→N and N→E the widest. M's vertex dropped from y14 to y17 to stop the middle reading hollow.

The suite — six variants

1

Primary lockup

logo/primary-lockup.svg — wordmark centred on the mark's full ink extent, not baseline-aligned. Clear space 12 units all round.
2

Stacked lockup

logo/stacked-lockup.svg — mobile chrome and square slots.
3

Icon mark

logo/icon-mark.svg — size-tested below.
4

Monochrome — light & dark

logo/monochrome.svg — one file, one hex to swap. It survives because the datum bar was separated from the bob by a gap, not by colour: the amber was never load-bearing.
5

Reversed

logo/reversed.svg — the amber is dropped, not lightened. On a saturated field an amber bar and a white word are two competing lights and the bar wins for no reason. 8.37:1 on brand.
6

Favicon — redrawn on 32

logo/favicon.svg — not the mark shrunk. Artwork bleeds to the grid edge, the suspension line goes 1.7px → 3px, the bar goes 2px → 3.2px, and every rounded corner is removed.

Size test — icon mark at 64 / 48 / 32 / 24 / 16, and the favicon at 32 / 16

64
48
32
24
16
fav 32
fav 16
At 24px the mark still reads as a hanging weight. At 16px the general mark loses its suspension line — which is exactly why the favicon is a separate drawing, and it still holds at 16.

Palette-neutrality proof — the same lockup on all six backgrounds

The mark is a fixed mid-luminance duotone: #17798B teal and #C2701C amber. Neither is currentColor and neither is a gradient. A theme logo ships as a data URL and cannot read page CSS, so it has to be provably legible on its own. Teal measures 5.13:1 on the lightest background in the set and 3.68:1 on the darkest; amber measures 4.61:1 and 4.10:1. Every element clears the 3:1 non-text bar at both extremes. A gradient was rejected because a gradient can hide a dead zone at one end and two flat mid-tones can be checked with a calculator.