This is the Apple /// Plus Owner’s Guide, which didn’t exist online until it was scanned and posted here. The physical copies that rarely appeared on eBay always commanded a high price.
This isn’t a technical reference, so there’s not a lot in the way of deep technical or troubleshooting information. Much of this manual will be familiar ground for anyone who has spent time using an Apple ///. Topics include using the System Configuration Program, SOS commands, working with drivers, and other basics, but there are some sections that cover /// Plus-specific topics such as the interlace switch, and there’s some good information in the appendices.