Science Experiment With Eggs

Question: What is the control for this science experiment?
I am having troubles with my homework. The experiment is:
Different masses are attached to the end of a spring and then is dropped at a certain height so that it hits an egg without breaking it.
I can’t figure out what the control for this type of experiment is!!!
HELP!
Answer: preform a trial to ensure the egg can break, to prove your not using some uber-egg.
the height is NOT the control, the height is a CONSTANT.
Egg in a Bottle Science Experiment