The Redstone Extractor is a generator added by Calculator. It generates Redstone Flux from items containing redstone (see table below) inserted in its top slot, and Furnace fuels inserted in its bottom slot.
It can hold up to 5000 redstone and consumes 400 of it every time its current Furnace fuel fully burns out, and will not burn a new one if there isn't enough redstone. Because of that, using longer burning fuels will result in a much lower usage of redstone.
