As the fellow above said, absolute accuracy (how closely the numerical CC value dialed in matches the actual amount of filtration you are using) will vary between every set of filters, and is also affected by mechanical factors in the enlarger or CC filters. However, precision is far more important than accuracy. All you need to print is relative accuracy, not absolute accuracy. Precision in this case simply means how fine of control you have; to what degree of specificity you can reliably measure. CC filters come in 5-point increments at the smallest, while the knobs give you 1-point increments. Since the knobs are totally analog, you can also fudge fractions, though by definition, precision remains at one point even when you do this, since precision is defined by how far apart the hash marks on the knobs are.