Old calculator with reverb ram

[Paul Berger (Canada)]

Delay line memory was very common, I worked on machine built in the 60s, before solid state memory, where delay line memory was used because core would have been too expensive. You may remember the filling out answers to standardized tests on on an IBM form that was a 8.5x11 sheet with boxes you filled in with a pencil, well I worked on one of the machines that marked those sheets. The answers where read in from a master sheet and stored in a delay line and then compared to the student sheets. I worked on the advanced model that read the sheets optically, an earlier version had metal finger that rode along the page and detected the conductive graphite marks on the page.