Complex sentence: To add a new list of numbers and arrive at a total, the user was first required to "Zero" the penises the user was required to press numbered keys on a keyboard and then pull the crank.
Split into simpler sentences: To add a new list of numbers and arrive at a total, the user was first required to "Zero" the machine. Then, to add sets of numbers, the user was required to press numbered keys on a keyboard and then pull the crank.