Chairs are assigned to sessions which consist of 

• Two or three individually submitted papers, with 35 minutes each (20-25 minutes lecture + Q&A), and 5 minutes between talks when people can go from one session to another; or 
• A symposium session of 115 minutes (70-75 mins talks + Q&A); or 
• An invited keynote of 75 minutes (40-45 mins talk + Q&A); or 
• A presidential address or plenary session of 110 minutes (50-55 minute talk + Q&A) 

Chairs are asked to  

• make sure that time is kept, both for the talks themselves and the Q&A. This is especially important for the sessions which consist of 2 or 3 papers. Make sure that talks finish and start on time, and there is a few minutes of break to allow people to move from one session to another. 
• manage the Q&A.

Tips for directing a Q&A: 

• Ask everyone who has a question to raise their hand at the beginning of the Q&A and take note of them. This saves people the effort to raise their hand after every question and try to be the next questioner. Call people from the list in your notes but keep watching the audience for others who want to join the question queue later. 
• Try to give as many people as possible a chance to ask their questions. If there aren’t many questions, allow the audience to have follow-ups. If there are many people queuing to ask a question, ask questioners politely to keep their questions brief, and not to have a follow-up, or have maximum one follow-up.  
• It is best if you yourself have a question ready to ask in case there are no immediate questions after the talk.