An alchemist can add formulae to his book just like a wizard adds spells to his spellbook, using the same costs and time requirements.
But it's not mentioned same "Spellcraft check" so I'm confused.
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Alchemists aren't mentioned in the Spellcraft skill simply because the Alchemist wasn't around when the Core rules were written and it's never been updated.
The only key difference between a wizard learning and an alchemist is that alchemists do not need to decipher arcane writings before copying them.
Therefore, to copy a spell/formula to your formula book:
Note that you can take 10 on these checks if "your character is not in immediate danger or distracted".
Lvl Cost 0 5 gp 1 10 gp 2 40 gp 3 90 gp 4 160 gp 5 250 gp 6 360 gp 7 490 gp 8 640 gp 9 810 gp
Being a Wizard or an alchemist is expensive.