On the eve of Yom Kippur, the High Priest was brought to the Chamber of Avtinas to learn how to gather all of the granules of the incense from the vessel into his palms properly without assistance. He was also required to make an oath that he would not deviate from the instructions for the the incense service while alone in the Holy of Holies. This chamber was one of three places guarded by the priests. 
The Chamber of Vessels
Contents:   Part I,    Part II,    Part III,    Part IV,    Part V,    Part VI,    Part VII