How do you use the spell tracker on Lamentations of the Flame Princess character sheet?

On the official character sheet of Lamentations of the Flame Princess (and on some fan-made sheets as well), the spell tracker looks like this:

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How am I supposed to use this? I noticed that there’s a dot per spell level (cleric spells go up to level 7 and magic-user spells go up to level 9), but I still don’t understand.