Oldest computer you've used for "real work"?

[groundbeef]

I brought my slide rule (that I got from my grandfather) to work one day to show my boss. He insisted that we use it to calculate the value of a current limiting resistor on the high speed digitizer board we were building.

This isn't the oldest computer I used, but the coolest: In 1990ish as a co-op student, I spent a couple of weeks using a Cray XMP. It had 6 processors, 128 MB ram, 128MB solid state disk, and 56GB fixed disk.

One of the engineers where I worked set up a fluid dynamics FEA model and it was my job to run through several dozen scenarios and plot the results.

The model took about 4 hours to run on a VAX. So they moved it over to the Cray, where it took about a minute. Then I plotted the results on a graphics terminal over a 2400 baud dial up line - about 5 minutes for each screen to download, then did a screen dump to a wax printer.

Good times...