Carl's explosives manual, which warns the studio's simulations are only ranges of possibility.
When Carl learns that his Advanced Bomber's Studio simulator sometimes returns a range of possibilities rather than a single outcome, it is the cookbook that stresses the point: just because a bomb blew a certain way in the simulation is no guarantee it will actually go up that way, because thousands of small environmental factors affect a real detonation.
It functions as the authority behind his craft, tempering his confidence in the new room's virtual testing.
A crafting manual Carl consults for explosives theory.
Reference text warning Carl not to trust simulated results too far.