This means that you cannot use the S option to treat zero cells. When it is used, the missing distances should be entered as if present and the degree of replication for them should be given as 0. The quantity n is the number of times each distance has been replicated. In simple cases this is taken to be one, but the user can, as an option, specify the degree of replication for each distance. The distance is then assumed to be a mean of those replicates.
P is what distinguished the various methods.
An intermediate method is also available in which P is 1.0, and any other value of P, such as 4.0 or -2.3, can also be used. This generates a whole family of methods. All these methods make the assumptions of additivity and independent errors. The difference between the methods is how they weight departures of observed from expected. In effect, these methods differ in how they assume that the variance of measurement of a distance will rise as a function of the expected value of the distance.