It's actually about the SOL prototype as published with plans in the July 1976 issue of Popular Electronics. Probably only a single machine was ever completed,

It's actually about the SOL prototype as published with plans in the July 1976 issue of Popular Electronics. Probably only a single machine was ever completed, which was functional for a short period. A few PCBs were ordered, but the design was withdrawn in favor of what became the SOL 20 (with the authors, Bob Marsh and Lee Felsenstein, actively urging customers to wait for redesigned boards). Compare the first video in the series: https://www.youtube.com/watch?v=jYx0s8SBC9Q https://www.youtube.com/watch?v=jYx0s8SBC9Q