Two measured root causes on the headless engine, both silent:
1. page_setup_apply wrote PLOTSETTINGS group 147 (unit_factor) as 1.0 for
every scale. Under USE_STANDARD_SCALE AutoCAD's plot engine scales by
group 147 alone (a 1:10 sheet with code 21 and 147 = 1.0 plotted a
100-unit line at 99.99 mm while the row, `applied` and 142/143 said
1:10; patching 147 to 0.1 alone gave 9.99 mm). AutoCAD writes 147 as
numerator / denominator (measured live on AutoCAD 2026 for fit, 1:1,
1:2, 1:10, 1:50, 2:1, 10:1: 1.0, 1.0, 0.5, 0.1, 0.02, 2.0, 10.0). The
writer now stores 75, 142/143 and 147 from the one resolved ratio on
every route, so no reader can disagree with the plot.
2. DXF_STANDARD_SCALE_TYPE and _plot_scale followed ezdxf's STD_SCALES,
which has no 19 = 1:5 and numbers everything above 18 one lower than
the ObjectARX StdScaleType enum AutoCAD actually writes (1:10 = 21,
1:20 = 23, 1:50 = 26, 1:100 = 27, 2:1 = 28, 10:1 = 31 — measured via COM
SaveAs DXF). An AutoCAD-authored 1:50 sheet listed as "1:100" and a
1:10 sheet rendered at 1:16. papers.py now authors the full file enum
(DXF_STD_SCALES, codes 1-33 with AutoCAD's imperial names), the writer
uses the same codes ActiveX uses, and nothing goes through ezdxf's
table. 1:5 stays on the custom route on both engines (the live setter
refuses 19) while the reader knows code 19 for files AutoCAD wrote.
Tests: the plan's `1:50 -> 25` assertion was the stale numbering and now
pins 26; a pure-data test pins the enum against the measured codes and the
ActiveX numbering; a parametrised writer test checks 75/142/143/147 for
every catalogue scale; a reader test stores the scale exactly as AutoCAD
saves it (including codes 19 and 22 the writer never emits) and checks
page_setup_list and _paper_frame report and render it at its own scale.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
