Chamber air is then pumped continuously through 1.2cm. (i.d.) PVC tubing, usually at 15l./min. but the exact rate is determined by the anticipated moisture output of the bird. Relative humidity increases from about 60% to 7 5 % at the end of a 24 hr.measurement period. Room temperature(21 + 2°C) is controlled by an air conditioning unit; this helps to maintain constant temperatures within the chamber.