Burroughs Portable
"Though not a featherweight machine, the Portable lent itself to travel much better than its Class 3 cousins. It's weight of about 25 pounds must have felt exceptionally portable considering a full bodied Class 3 could easily weigh in over 50 pounds."
Source: Dr. Tim Bergin, Eric Ashman, Seth Gordon, Jeana Scheirer, Dave Muehling and Andrew Hewitt, "Mechanical Computing."

X-Number World of Calculators