I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer."? 

How did the Z2 get the letter portion of its name?