225 ILCS 705/4.07
Every State Mine Inspector in his regular examination of mines shall measure with an anemometer the amount of air passing in the last crosscut in each pair of entries. He shall also investigate the condition of ventilation in all working places to see that ventilation is adequate, and in longwall mines the last face of each division. He shall measure with an anemometer the amount of air passing at the inlet and outlet of the mines. He shall compare all such air measurements with the last report of the mine examiner and the mine manager, in the mine examination book of the mine. He must verify that the legal code of signals between the engineer and the top man and the bottom man has been established and is conspicuously posted for the information of all employees.
225 ILCS 705/4.07