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Stats -> Level-Up Mechanics
As I understand it, the only statistic that has a compounding effect with level-ups is Constitution. In other words, the effect of Constitution on HP between a player who has 18 CON from level 1-5 and one who has 10 CON from level 1-5 and then suddenly has 18 at level 5 would be different, because the effect of CON on HP gained per level is computed at the moment of each level-up and is not modified retroactively if CON is modified.
Are there any other statistics that have this effect? For example, are the effects of INT and WIS on spells known computed at level-up, or are their effects "instantaneous" at each level?