One can understand the d/3 expression as it represents the thirds of nail length. But why we add clinical form to hyperkeratosis? The answer is that we see hyperkeratosis has some influence on the treatment design and outcome, but the impact of this is not directly proportional as in the case of depth. The share of hyperkeratosis in clinical index component will increase with the depth of involvement, as it is seen in clinical practice.
In SWO and PSO, to evade calculation of hyperkeratosis where it is absent and depth of involvement where it is not applicable or fixed, we further made the equation of a kind:

Using this sophisticated formula we achieved that in each case of SWO clinical component has fixed value of 1.
In each case of PSO it is also fiixed and equals 3.
In DLSO clinical component is represented by increasing range of values from 1 to 5.