I remember participating in a study that the State of Washington was doing back in the early 80s, when they were trying to establish (or maybe it was to validate - it's been a long time) a comparative worth study to be used to set wage rates. The two occupations they were focusing on were licensed practical nurses (one year of formal [classroom and clinical] education required, life-and-death responsibilities) and heavy equipment [i.e., bulldozer] operator (some practical training and much OJT, potential to do significant physical damage). The conclusion was that it was rather like trying to compare apples and weather balloons, and they went off in another direction.

IMHO - and I've been there - a manager really should be able to do, to supervise and to teach everything that an subordinate does. This isn't always possible, especially in cases of technical skills, but the key function of management is to integrate diversity into cohesion.