One Quarter Must Refer To The Coin
Instructions for changing the battery on a heart rate monitor:
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The coin-slot starts in the horizontal position; notice that the text says "one quarter turn," but the image is actually a one-eighth turn.
It opens on a one-eighth turn, but it will helpfully turn a full quarter turn in case you're wondering. Which passes the point where the little locking things pass through the gaps. One quarter turn results in locking it again.
Technical writers are cretins.