Mystery Architecture

Mystery Architecture 
Q: If a student checks the tower with their own ball do they then take the ball off for the judge to place their tennis ball? Are students allowed to steady the tower as the judge placed the tennis ball, prior to measuring?
A: Please read the event description:
“Students may bring their own tennis ball just for testing purposes during the competition”.  
“They will be provided with the Supervisor’s tennis ball (which will be used for all measurements) and that should be balanced by the students on top of their tower. Since no building materials are to extend above it, the top of the tennis ball will be considered the highest point of the tower. The tower must remain standing until the measurements are recorded”.