The majority of these exercises occurred in two simulators: the Command Module simulator and the Lunar Module simulator. A big hurdle to running the simulations was computing power. The earliest simulators, some of which were adapted from Gemini equipment, were run on analog computers. It was a big milestone when they had expanded the operation to 10 computers, and another feat when they switched to digital. Here’s two of the simulators on March 1, 1968.