Shiv: Reinforcement is a training manual found in the chapter "Pittsburgh".
Overview[]
Obtaining this manual improves the durability of shivs that Joel can craft. If you missed the first manual on shiv durability, each shiv can now be used twice on human and infected enemies. If you did obtain the first shiv upgrade in Bill's Town, each shiv can now be used three times.
Shiv Doors, however, will still break shivs upon being opened, and they must be opened with a full, unused shiv.
Location[]
To obtain this manual, you need to find the Note to Staff first, which contains the combination to a safe. On the ground floor of the hotel, there will be a safe in the lobby, which can be unlocked using the combination in the note. The manual will be inside this safe.