# Differential-element verification

## Visual refresh - 2026-10-11

Reviewed the current fluid and differential-element modules. Two-boundary
element dimensions now use external inward `->|` and `|<-` arrows, including
Cartesian spans and projected slice thicknesses. Fluid pressure-element
`dx` follows the same convention. The rotating tube now has thickness arrows;
its slice uses configurable hatching through `every fluid element` and
`every physics fluid element`. Font inheritance and native line widths remain
unchanged. The cylindrical shell's radial marker sits above the projected
rim with extension lines to its two boundaries. The font gallery has a deliberate page break before material styles.

- All 16 `l3build` suites pass; all 58 examples compile.
- All 18 element invalid-input cases and 16 combined element/fluid cases
  produce the intended diagnostics.
- All 122 generated feature references and the single-file runtime are current.
- All 20 isolated bundle checks pass at the 5-million-word memory limit.
- Visually inspected all 14 fluid assemblies, composed reference scenes,
  native fluid nodes, material patterns, circular/solid elements, the font
  gallery and projected percentage coordinates (eight PDFs, 26 pages).
- A separate rendered styling probe checks large labels, thin rotating slices,
  dots and solid-fill overrides, including the collision-safe style alias.
- The updated manual compiles to 92 pages. Changed element and fluid pages
  are rendered for inspection; the existing enumitem negative-labelwidth
  warning remains, with no overfull boxes or unresolved references.

Evidence: `tmp/fluid-elements-20261011/`, plus the existing verification
script output directories. Refreshed runtime and guides are in
`output/overleaf/`; current PDFs are in `output/pdf/`.

Validation against the final 1.7.0 checkout on 2026-09-30. CTAN submission and
publication status are recorded separately in `release-1.7.0.md`.

- All 15 regression suites pass. Generated reference and bundle freshness
  checks pass for 121 features.
- All 57 example documents compile (154 rendered pages) with the checkout
  forced through `TEXINPUTS`; each example has its own output directory.
- The isolated single-file runtime compiles eight module gallery documents
  and the six-page starter, using an empty user TeX tree. Recorders contain
  only the local bundled `tikzphysics.sty`, with no split physics libraries.
  Explicit meta/module/heattransfer alias requests also compile without
  loading system copies.
- All 17 module gallery pages are pixel-identical between split and isolated
  bundled runtimes at 72 dpi. Every sampled RGB pixel is monochrome.
- Every page of the thermodynamics, thermalphysics and elements galleries
  was visually inspected after the final runtime changes.
- Physical strokes inherit native TikZ line widths. A regression instrumenting
  actual PGF stroke calls verifies 1.25 pt document styling across mechanics,
  surfaces, ramps, optics, differential elements, fluids, thermodynamics and
  thermalphysics. No physical runtime imposes a custom stroke width; debug
  annotation leader lines retain their independent diagnostic styling.
- Overleaf archive integrity and the contents of all 20 files are checked.

Evidence: `tmp/release-1.7.0/` (compile recorders, raster comparisons, visual
renders, complete test output and independent loading probes).

Element fixtures contain 57 existing polar PASS records, 23 solid-element
records (including both x and y in point comparisons), and 81 new review
records. The added fixture checks all integer families on nine native nodes,
all 13 new projected pic families, independently calculated large-radius and
narrow-angle centroids, mixed units and transformations, axial endpoints,
unequal cone slice radii, ellipse interior points and instance isolation.
All 18 invalid-input cases produce the intended package diagnostic.

The four element PDFs contain six visually reviewed pages: original circular,
solid and font/material galleries plus three new percentage/styling pages.
Fixed the reproducible 3 cm polar-centroid overflow using normalized radii;
small-angle sinc uses a stable limit. Corrected vertical sphere-disk hidden
edges, cylinder-shell physical height, and native element text centring.
Added actual projected rim and axial percentage coordinates, preserving named
components and existing family directions. Label leaders in the new gallery
prevent crowded percentage annotations.

Full-circle compass anchors are placement bounds; rim families locate actual
material curves. Highlighted finite-thickness slices and unwrapped rings
illustrate differential approximations, not exact finite-volume solvers.