Editing List of BBC test cards (section)

==Test Card A==
Test Card A was introduced in 1936–37. However, it was only broadcast as engineering tests<ref name=":1">{{Cite book |last=HERSEE |first=G. |url=https://www.worldradiohistory.com/UK/BBC/BBC-Books/bbc_monograph_69.pdf |title=BBC Engineering Department Monograph, Number 69 |date=September 1967 |publisher=BBC |pages=6}}</ref> from January to (approx.) October 1947, when it was replaced by the first version of Test Card C. An electronically generated "cruciform" test card (or "art bars") was often shown instead of Test Card A until well into the 1960s.<ref>https://web.archive.org/web/20160716000423/http://www.pembers.freeserve.co.uk/Test-Cards/index.html#405-Lines {{Bare URL inline|date=August 2024}}</ref><ref name=":1" />

The test card was designed to test for focus, frequency response and scan geometry.<ref>HERSEE, G. (September 1967). ''[https://www.worldradiohistory.com/UK/BBC/BBC-Books/bbc_monograph_69.pdf BBC Engineering Department Monograph], Number 69'' (PDF). BBC. p.&nbsp;5.</ref> High frequency response is indicated by gratings corresponding to 1, 1.5, 2, 2.5 and 3 MHz; while low frequency response is indicated by a solid black bar below the central circle.