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HI Sub.
Yep, you're right. The crayfords have 2 knobs, 1 on either side, or a large one and a smaller one on the same side.
The larger knob will be the "coarse" adjustment, where you want to rack in or out quickly. The smaller/fine adjustment knob is the "micro", where it's geared at a 10:1 ratio - so one revolution of the large knob results in 10 revolutions of the smaller knob.
In reverse, it means small adjustments of the micro knob will hardly move the large knob and can be used for very small adjustments in focus to get it "just right". It also helps eliminate the scope shaking around as you focus because it's a smoother action.
By the way, the 10:1 focusers are great! Definitely worth the upgrade if the scope doesn't already come with it.
HTH
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