Minecraft wiki entry for Calculator, associated text: Redstone
Mechanics/Redstone/Circuit
Redstone clock
Mechanics/Redstone/Logic circuit
Mechanics/Redstone/Memory circuit
Mechanics/Redstone/Pulse circuit
Mechanics/Redstone/Transmission circuit
Tutorials/Advanced redstone circuits
Tutorials/Arithmetic logic
Tutorials/Basic logic gates
Tutorials/Hourly clock
Tutorials/Redstone computers