The work, including the code you developed 3 years ago was accepted and paid-for when it was delivered. If there was a requirement for documentation, then it was met, else you wouldn't have been paid. Now comes the former client, wishing you to provide more than he agreed to pay for.

The logical response, if I were in your situation, would be, "Bring money."

Documentation can easily be as much as 95% of a project's cost. If a client wants documentation tracing each routine in the code and each module of the hardware back to system requirements, which should always be thoroughly documented, and has only now realized that he wants that, then he should be prepared to pay for it now.

Too many clients are allowed to "get by" with a simple demand the the work product "works" without precisely specifying in picovolts and femtoseconds, what, exactly, "works" means.

In the interest of maintaining your relationship with this particular client, you may wish to deviate somewhat from the general approach I've pointed out here, but ... he's really asking for work product he once wasn't willing to pay for. If you're being asked, essentially, to train your successor/competitor in what he should be able to do on his own, then someone should compensate you for your time, effort, and involvement. Your successor/competitor has agreed to take on a task of which he's apparently incapable, i.e. understanding the materials and characteristics of a project he's agreed to reverse-engineer. Your former client has apparently determined that this person is the one he wants to do the work. You can agree to help him, for compensation, of course, or let him stew in a soup of his own making. After all, if he'd paid for the doc's up front, you'd have provided them.

One word of caution ... Do NOT, tempting as it might be ... I repeat ... DO NOT ... allow the resolution of this client request degenerate into, "Have your new engineer call me and I'll explain ..." because that will allow him consume an endless amount of your unpaid/underpaid time and resources. Remember, too, that the currency has inflated considerably since you did the original work.

Simply tell him, "My hourly rate is $<insert appropriate amount here> and you'll be billed for a minimum of 30 minutes for each phone call or other contact, plus <insert amount here> per line of written text and <insert amount here> per line of code/pseudocode. This could have been done at much lower cost at the outset, but that didn't coincide with your wishes at that time. It's time to pay the fiddler." Keep careful logs of every contact, including time, duration, and person contacted, and send a bill. Refuse further non-negotiation contacts until there's a substantial retainer in his account.

RE