Constancy
Constant, Unchanging
noun
Keeping things constant and normal ensures constancy.
恒常 is a formal word used to describe something that remains constant and unchanging.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
このシステムで部屋の温度を恒常に保っています。
With this system we can consistently keep it at room temperature.