Here we have a typical older style coin meter from the U.K.

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After the coin box has been removed, the ring which holds the coin mechanism in place can be unscrewed:

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There is an internal broad A/B rate setting, but then smaller adjustments to the rate can be made by simply re-inserting the coin mechanism with the index mark aligned to the required number. This just determines how far the handle must be turned for the coin to drop into the box, and thus how far the cog is turned for each coin deposit:

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Don't be fooled by the 1985 calibration sticker or the "50p. coins" markings. The coin mechanisms were changed over the years to allow for higher value coins. Peeling off the sticker from the coin box reveals this meter's true vintage:

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