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The title, contrary to popular belief, does not come from the cars used, as in Ford Zephyr and Ford Zodiac. In fact, the Zodiac was never used by British police, whereas the Zephyr was the standard patrol traffic car (not the same as "crime car") used by Lancashire and other police forces. The term comes from the radio call signs allocated by Lancashire Constabulary; Lancashire police divisions were lettered from north to the south, "A" Division (based in Ulverston) was the detached part of Lancashire at the time around Barrow-in-Furness, "B" Division was Lancaster, and so on. Letters further into the alphabet were in the south around the Manchester and Liverpool areas. The TV series took the non-existent signs Z-Victor 1 and Z-Victor 2.