A "DDD Alignment System" is an alignment system using a "Digitial Diagnostic Disk(ette)" The DDD is a very special diskette that has various tracks and sectors recorded on the disk intentionally misaligned. By knowing how the disk was made (which sectors were misaligned, in which direction, and by how much), and by seeing which sectors can and cannot be read, the exact alignment status of a drive can be tested without an oscilloscope or any other test equipment. All that you need is the DDD disk and a software program that matches the disk and the disk controller of the target system. Dysan made these, and perhaps others did also. I have some here for 8" and 5.25" drives. They are good for checking the alignment, but they are kind of useless for actually adjusting it if it's off. However, my recollection is that they ALSO have the analog "cats eye" tracks on them for alignment with an oscilloscope.