Why don't speedometers highlight the most important speeds, like 30mph?

Why can't cars sold in the UK have speedometers that highlight the most important speed limits, e.g. 30 mph, in numbers instead of a trying to align a needle with a small blob of paint? I've stuck a 30 sticker over the blob, to make it more easy to read and thus stay legal, but why can't manufacturers come up with a more sophisticated solution?

Asked on 15 May 2017 by T. Furness

Answered by Honest John
Because most cars in the world have kilometre speedos and that's what they are designed to have. A mpg speedo face is a compromise. They have come up with a solution which is big, digital speedos, bit a lot of drivers still prefer hard to read clocks.
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