[R] what does Height represent?

[zhaoshi]

hi--

I am new to R and try to use R cluster my binary data. I use 
hierarchical clustering
plot (hclust (dist(x,method="binary"),method="average"),cex=0.1)
I end up with a cluster Dendrogram. On the left of my dendrogram, there 
is scale called Height from 0.0 to 1.0.
I don't understand what does Height represent. If the Height represents 
the distance scale between two different data point,
it looks like if I add up the length of each branch, I end up with 
distance of some pairs > 1. It is not possible the distance
between any data point will greater than 1. Could some help me out?
 
Thanks


Zhaoshi