The marble mihrab is similar to the one in the main qibla iwan of mosque. A "mihrab" indicates the direction of the "qibla" for prayer. The mosque is entered through a door situated in the qibla wall, near the minaret. This determined the Qibla, or Muslim direction of prayer. One must also make sure to face the Qibla (direction of prayer), whilst making du'a. The "Qibla" is the direction faced during prayer. Jerusalem served as the first qibla (direction of prayer) for Muslims. The qibla of the Mosque projects towards the reservoir by about . Ornate qibla compasses date back at least to the 18th century. This determined the "Qibla," or Muslim direction of prayer. One application involved determining the "Qibla", the direction to face during prayer. Today spherical trigonometry also underlies nearly all application or websites which calculate the qibla. The seven naves parallel to the qibla wall includes seven bays. For example, the qibla from Alaska obtained through spherical trigonometry is almost due north. The determination of qibla was an important problem for Muslim communities throughout history.