Simpson's study was followed by a study by Schutrum et al.[15] in 1961, and more recently a study by van Schijndel et al.[16] in 2003. These studies have focused on providing detailed measurements of the quantities of air and heat transferred inside the compartments of a door as it revolves. With the exception of the study by van Schijndel et al., which was purely theoretical, the measurements carried out for the other studies were used to provide design charts enabling engineers to estimate the quantity of air transferred by a door in function of the revolution rate and temperature contrast.