Also, the Yahoo group for the Pro III is an excellent place to ask questions, especially on operation. Adam, VA7OJ, is truly an expert on the Icom 756 lineup, especially the Pro III, and he is the moderator of that group. He also maintains a web site which is a gold mine of technical information on the Pro III. The web site link is:
http://www.ab4oj.com. I believe that AB4OJ is his US callsign. After bringing up the page, you will find a link to his Icom page.