Timeline:
After 2016 Rio Olympics - Coaching (shouting instructions) between rallies at anytime during games are allowed (authorized coach only).
After 2012 London Olympics - Ball size increased to plastic 40+mm replacing celluloid 40mm.
After 2008 Beijing Olympics - Speed Glueing is Banned.
After 2004 Athens Olympics - Ball size increased to celluloid 40mm replacing celluloid 38mm.
Links:
ITTF Handbook
Tabletenniscoaching.com
ITTF Athletes Commission
