Product support is essential.  As I have intimated, many of us analog circuit designers were schooled some time ago and it is my experiance that each day more analog circuit design guys leave the employment market than join it.  More often than not, they leave products behind. 

It is also a truism that engineers as a group do not like to write.  This often means that the projects that are left behind are simply not well understood by those whose job it now is to build, modify or otherwise understand the product. 

I can help.  Send me the circuit that needs to be understood along with everything else that you are comfortable showing me about your product and I will write a description of the function of that circuit.  I will do so to the level we agree on.  This includes everything from simple description of the circuit concept to a thorough analysis including expected mean values on outputs including the standard deviation of the output for SPC (Statistical Process Control) purposes.