Couldn’t resist this one when I saw it on the shelf at Deseret for $3 a few weeks ago, so I snatched it up. The thing was *filthy*, but seemed to be intact, although it was so gummed up that the lever wouldn’t pull. I’ve currently got it working now, but it still needs another … Continue reading Mechanical Calculator: 1963 Underwood-Olivetti Summa Prima 20