longitude difference used was off by three degrees. Accurate longitude values in the Islamic world were available only after the application of cartographic surveys in the 18th and 19th centuries. Modern coordinates, along with new technologies such as GPS satellites and electronic instruments, resulted in the development of practical instruments to calculate the qibla. The qibla found using modern instruments might differ from the direction of mosques, because a mosque might be built before the advent of modern data, and orientation inaccuracies might have been introduced during the building process of modern mosques. When this is known, sometimes the direction of the mosque's mihrab is still observed, and sometimes a marker is added (such as lines drawn in the mosque) that can be followed instead of the mihrab. Instruments Muslims use various instruments to find the qibla direction when not near a mosque. The qibla compass is a magnetic compass which includes a table or a list of qibla angles from major settlements. Some electronic versions use satellite coordinates to calculate and indicate the qibla automatically. Qibla compasses have existed since around 1300, supplemented by the list of qibla angles often written on the instruments themselves. Hotel rooms with Muslim guests may use a sticker showing the qibla on the ceiling or a drawer. With the advent of computing, various mobile apps and websites use formulae to calculate the qibla for their users. Diversity Early Islamic world Because varying methods have been used to determine the qibla, mosques were built throughout history in different directions, including some that still stand today. Methods based on astronomy and mathematics were not always used, and the same determination method could yield different qiblas due to differences in the accuracy of data and calculations. Egyptian historian Al-Maqrizi (d. 1442) recorded various qibla angles used in Cairo at the time: 90° (due east), 117° (winter sunrise, the "qibla of the sahaba"), 127° (calculated by astronomers, such as Ibn Yunus), 141° (Mosque of Ibn Tulun), 156° (the rising point of Suhayl/Canopus), 180° (due south, emulating the qibla of Muhammad in Medina), and 204° (the setting point of Canopus). The modern qibla for Cairo is 135°, which was not known at the time. This diversity also results in the non-uniform layout in Cairo's districts, because the streets are often oriented according to the varying orientation of the mosques. Historical records also indicate the diversity of qiblas in