Uterine contractions are clinically palpable when there intensity is more than?

Uterine contractions are palpable when intensity exceeds 10 mmHg Uterine contractions become painful when intensity exceeds 15 mmHg Intrauterine pressure at which uterus becomes hard that it cannot be indented by figure -40 mmHg. Ref: Williams Obs 24e pg 498.