To determine a best length of strings (K) in our model, we plot the mean value of X over all K-strings from a genome (whole DNA sequences or protein sequences) as a function of K (see Figure 1 for examples from our data). The mean value of X starts to approach zero at K = 6 or 7 if we use protein sequences from genome and at K = 11 or 12 if we use whole DNA sequence. The mean value of X being close to zero means that the value of p (from the sequence) is almost equal to value of q (from the model). Hence these K values are suitable for phylogeny reconstruction using our approach. This result is also confirmed later in this paper from a biological point of view. 