On the wiki page of (https://www.mothur.org/wiki/Dist.seqs), it was mentioned that [The length of the shorter sequence is 10 nt, since the gap is considered as a single position. Therefore the distance would be 3/10 or 0.30. This is the distance calculating method employed by Sogin et al. (1995).]
However, I could not find this article published in 1995. I read the article of (The Effects of Alignment Quality, Distance Calculation Method, Sequence Filtering, and Region on the Analysis of 16S rRNA Gene-Based Studies). The Sogin et al. (1995) does not appear in the references section .