The main difference between a manipulation and an adjustment is the degree of specificity. An adjustment by nature must be unilateral along a predetermined reduction pathway vector. This must be appreciated as a major difference within the term adjustment. Some have evolved to using non-excursion percussion force to replace vertebrae in the upC spine. Adjustments require x-ray measurement, for to see is to know and not to see is to guess.
Manipulation is awesome for supportive soft tissue.
Precision adjustments can be incredible for restoration of health and maintenance of same. In some areas of the spine manipulation can be repeated indefinitely on a reasonable time schedule without harm and with supportive soft tissue benefit. An adjustment can only be delivered in the presence of neuro disturbing vertebral displacement. An adjustment can only be given in the presence of neuro-aberration. For greater precision, the art of adjusting the spine has evolved into the use of floor mounted instruments upon which an alignee lays and is adjusted.