Work the five delivered sources into the pages

The source-request loop paid for itself immediately — two of the five
corrected something rather than confirming it.

The Economist piece settles V1, the riskiest live claim, but our note
had over-claimed: truncating the scale is its *first* example, not one
of "several." Note rewritten to quote her. The same article turned out
to contain a dual-axis chart she caught herself on, now cited.

Datawrapper's color-scale part 1 refuted the assumption behind a queued
sin outright: it makes no argument against rainbow scales and endorses
multi-hue sequential gradients. The rainbow entry is now marked as
having no verified source at all, rather than ample backing.

The dual-axis post independently draws the same line we drew last turn
— of four uses only the alternative-scale case survives, their example
being F against C — and led to two references worth more than the blog
post: the Isenberg et al. study that tested dual-scale charts, and Few's
article working through the cases. Both ship without full metadata
rather than guessed metadata; queued.

Pie and stacked posts gave verbatim support, plus one correction: a
100%-stacked chart has two readable baselines, not one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ULE5RRxdQE1ebwefEd2eCM

docs/sources/datawrapper-dual-axis.md

@@ -0,0 +1,70 @@
+# Datawrapper — "Why not to use two axes, and what to use instead"
+
+Lisa Charlotte Muth, `blog.datawrapper.de/dualaxis/`, published **8 May 2018**,
+intro updated **July 2026**. Supplied as PDF, read 2026-08-05.
+Answers queue rows 2 and (partly) 1.
+
+## The July 2026 revision, verbatim
+
+> We originally published this article in May 2018 to explain why you couldn't
+> create dual-axis charts in Datawrapper. Since then, we've changed our minds.
+> We've learned that in some cases, dual-axis charts really are the best way to
+> show the data — and that people who've learned to read them correctly (in
+> financial services, for example) aren't misled by them. […] But all the issues
+> this original article pointed out are still valid. A general audience is
+> indeed likely to misread dual-axis charts.
+
+So: audience-dependent, not a reversal. They now ship the feature on a Business
+plan and kept the article standing. They also link a newer piece, "What to
+consider when creating dual-axis charts" (23 July 2026), not supplied here.
+
+## They draw the same line we drew
+
+The article lists four reasons people reach for dual axes, then says:
+
+> of these four use cases, we think that only the last dual axis chart can be
+> used without being potentially misleading, since it only uses the second
+> Y-axis to show an alternative scale and not a second data series.
+
+The fourth case is **Fahrenheit and Celsius on one series** — the same example
+our sin page arrived at independently. Their test and ours match: the sin is a
+second *data series*, not a second *scale*.
+
+## The three problems
+
+1. **"Zero baselines at different heights can mislead."** The proportions are
+   arbitrary. Their worked example: German vs global GDP looks like it rises at
+   the same rate; extended to zero, global rose 80% and Germany 40%.
+2. **"Even zero baselines at the same height can mislead"** — "humans have a
+   tendency to set things in relation if they're close-by." Readers conclude
+   German GDP exceeded global GDP, then crossed in 2011.
+3. **"They're just hard to read."**
+
+Nutshell line: *"The scales of dual axis charts are arbitrary and can therefore
+(deliberately) mislead readers about the relationship between the two data
+series."*
+
+## The empirical source behind it — worth citing directly
+
+Isenberg, Bezerianos, Dragicevic & Fekete (2011), *A Study on Dual-Scale Data
+Charts*. 15 participants, four chart types; the dual-axis ("superimposed")
+chart was quoted as:
+
+> We found across the board that the superimposed chart performed poorly both
+> in terms of accuracy and time. […] it was ranked lowest by all but one
+> participant. Participants called it very confusing and demanding too much
+> concentration or reflection to decipher the non-monotonic and discontinuous
+> nature of the two scales.
+
+Added to the reference list as `isenberg2011`. Venue/DOI still needed — queued.
+
+Also flagged: Stephen Few, *Dual-Scaled Axes in Graphs: Are They Ever the Best
+Solution?*, which per Datawrapper concludes he "cannot think of a situation that
+warrants them in light of other, better solutions." Added as `fewdualaxes`;
+year and URL queued.
+
+## Alternatives they give
+
+Side-by-side charts; indexed charts (with Knaflic's caveat that this fails when
+one series moves +10000% and the other +5%); prioritise-and-label; connected
+scatterplot. Our page's repentance already recommends the first two.