  We investigate the asymptotic standard deviation of the Longest Common
Subsequence (LCS) of two independent i.i.d. sequences of length n. The first
sequence is drawn from a three letter alphabet {0,1,a}, whilst the second
sequence is binary. The main result of this article is that in this asymmetric
case, the standard deviation of the length of the LCS is of order square root
of n. This confirms Waterman's conjecture for this special case. Our result
seems to indicate that in many other situations the order of the standard
deviation is also square root of n.
