And I thought I had worked on some hairy old code: kottke.org passes on the story of a 1948 vintage plugboard computer still in use (at least as of last year): Don't mess with Texas's old computers
Sparkler's IBM 402 is not a traditional computer, but an automated electromechanical tabulator that can be programmed (or more accurately, wired) to print out certain results based on values encoded into stacks of 80-column Hollerith-type punched cards.
Companies traditionally used the 402 for accounting, since the machine could take a long list of numbers, add them up, and print a detailed written report. In a sense, you could consider it a 3000-pound spreadsheet machine.