Original sentence: Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about , equal to the  partial pressure of oxygen in the Earth's atmosphere at sea level, plus  CO2 and  water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation.In spacesuits that use 20.7 kPa, the astronaut gets only 20.7 kPa - 11.7 kPa = 9.0 kPa of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of  above sea level.The latter two figures add to 11.6 kPa (87 torr, 1.7 psi), which is why many modern spacesuits do not use 20.7 kPa, but 32.4 kPa (this is a slight overcorrection, as alveolar partial pressures at sea level are slightly less than the former)
Edited sentence: Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about , equal to the  partial pressure of oxygen in the Earth's atmosphere at sea level, plus   and  water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation.In spacesuits that use 20.7 kPa, the astronaut gets only 20.7 kPa − 11.7 kPa =  of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of  above sea level.The latter two figures add to 11.6 kPa (87 Torr, 1.7 psi), which is why many modern spacesuits do not use , but  (this is a slight overcorrection, as alveolar partial pressures at sea level are slightly less than the former)