Determination of performance levels - process substantially subjective therefore relevant requirements to experts (professionalism, experience, objectivity, moral qualities are imposed. Besides, performance level cannot be calculated on the example of one worker, it is result of supervision over group of performers and it turns out after processing of statistical data.
the actual qualification of the worker - ability not only to carry out the direct duties, but also to participate in the solution of production problems, to understand any aspect of economic activity of the enterprise. Such workers receive the fixed salary for qualification.
Probably, similar range existed long since, in any case at Taylor, however abilities of the worker to carry out norm mostly were estimated by the principle - it carries out it or does not carry out (or yes, or is not present).