Since some enchantments are more likely to appear at certain levels, this spellbox allows you to use levers to block bookshelves so that enchantments with the desired level appear more often.

Depending on which switch you flip, 1,2,4 or 8 bookshelves are blocked. The more bookshelves are blocked the lower is the enchantment level. So you can block 1, 2, 3, 4, and so on up to 15 bookshelves to get to the desired enchantment level.
To find out the ideal level, you can use this website: http://minecraftenchantmentcalculator.com/rev5/

Instructions:

You need 15:bookshelves
5:Pistons
1:Sticky piston
4:Lever
4:Redstone lamps
4:Signs
3:Redstone
1:Redstone Torch
1:Redstone Amplifier
1:Magic table
The rest:Obvious
Size:7x6x6
The numbers 4;2;1;8 are written individually on the plates.