The Challenger 1P Technical Report
I have a couple of these Ohio Scientific computers in my collection, namely the Challenger 1P and Challenger 4P. The former was accompanied by three manuals, namely The SUPERBOARD II/CHALLENGER 1P User Manual, The 8k BASIC-in-ROM Reference Manual and The CHALLENGER 1P Technical Report. The first two are common on the Internet in various repositories, but the last one didn't seem to be archived anywhere so I scanned it.
It's an interesting document in that it is as much a comparison of the Challenger 1P with other unnamed (but easily guessed) computers of the day, than it is a description of the hardware. Anyway, it's available at the link below...
Click to download The CHALLENGER 1P Technical Report (PDF)
25th December, 2016