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In order to see clearly at distance, it is necessary to move focus backwards to the macula by means of a concave lens (minus). Naturally, you would not move focus behind the macula, because that would put the eye into an active state of accommodation, which is unnecessary.
The weakest minus lens providing the very best visual acuity, is a measure of the degree of myopia and is also the notation of the refraction. Remember weakest minus!