For Quanta, Max G. Levy and Michael Moyer ask, “what is analog computing?” A timely question as data centres strain global power grids, the duo runs through the gamut of mechanical devices that solve complex calculations without the same hunger for energy—from the 200 BCE Antikythera mechanism to the 20th century differential analyzer (image). “Perhaps, by reaching back to computing’s past, researchers will be able to steer a sustainable path toward our computational future,” they conclude.