In the overview section of the docs
(http://www.clarkware.com/software/JDepend.html#overview) the term
Instability is described as:

"The ratio of efferent coupling (Ce) to total coupling (Ce / (Ce + Ca))"

This is misleading because the first parenthesis describes the first
term of the ratio whereas the second parenthesis describes the ratio
itself rather than simply the second term. I'd suggest applying one or
both of the following options to remedy the situation:

Drop the (Ce) or change the second parenthesis to (Ce + Ca).
Add a final phrase " giving I = Ce / (Ce + Ca)"

Rob