While drawing graphs that compare the silhouette measure of different clustering algorithms, what unit should I specify for the silhouette width?
Don't use the Silhouette measure for arbitrary clustering algorithms. In particular, don't use it for clustering algorithms which can produce non-convex clusters.
On data sets such as this:
the silhouette may be misleading.
The silhouette coefficient and silhouette plots are meant to compare different results of the same, convex, clustering algorithm (e.g. k-means).