Steadiness (5)
'steadiness' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for balance that I've seen before include "Weighing apparatus" , "State of equilibrium" , "A steady position as on scales" , "Rest" , "Surplus" .)
(Other definitions for poise that I've seen before include "Aplomb" , "Balance; composure" , "Sang-froid" , "Dignity and assurance of manner" , "Self-confidence" .)