People who over time recorded these votes, they had to check for vote tallies ending in 999 which were always suspect because that meant typically that the trip was not rolling over from 999 to 000 so that's one of the flaws and the other was, of course, the large size of the machine and the complexity in servicing such a thing and then moving it and storing it.
Source
Interview with Larry Bird, Smithsonian Institution's National Museum of American History, May 31, 2006.