The Muslim rulers made an effort to maintain fairness by measuring the level of water of the River Nile to determine the collection of produce as taxes from the farmland.
Produce from land that is flooded by the Nile differs from that from land which is difficult to irrigate. To measure the Nile's flooding, various Nilometers were placed along the river including the ones in Ansana, Manf, and Qasr al-Shama'. As these Nilometers stopped being used in AH 247 (AD 861), only the one which is installed on Roda Island is still operational.
The employee responsible for measuring the level of water was known as "Sahib al-Miqyas," or "the man of the Nilometer." He measured the increase in the Nilometer daily between afternoon and sunset. He also compared the increase in water level on each day with the same day of the previous year.
He recorded the results in a document sent to the high authorities. If there was a decrease in the inundation, this was kept secret from the people. When the water level reached 16 cubits or 8.4 meters or 27.5 feet, he would inform the people of the happy news, and they would celebrate the increase in the flooding