Atkinson resistance is commonly used in mine ventilation to characterise the resistance to airflow of a duct of irregular size and shape, such as a mine roadway. It has the symbol and is used in the square law for pressure drop, where (in English units) * is pressure drop (pounds per square foot), * is the air density in the duct (pounds per cubic foot), * is the standard air density (0.075 pound per cubic foot), * is the resistance (atkinsons), * is the rate of flow of air (thousands of cubic feet per second). where in which in addition to the terms defined above. where