The Washington arms control summit opens today. This chart has been prepared to help readers understand both the record of arms control agreement to date and the arms-related issues that still confront Mr. Reagan and Mr. Gorbachev. Four major areas are included. To use the chart, begin in the left-hand ``Issue'' column of any of the four areas and go horizontally across the ``Soviet'' and ``US'' columns. All of the column numbers correspond. A blank space indicates that no significant concession was made, or was necessary.