Sonar is an acronym (like radar, now spelled with all lower-case letters) for sound navigation and ranging. The principle involves bouncing acoustic waves off of objects, and determining their distances by measuring the time for the echoes to return. Sonar is commonly used on board ships and boats to measure the depths of bodies of water. It can also be used to locate underwater objects such as fish, submarines, and the shipwrecks of Spanish galleons. A complete sonar set has several components, including an acoustic pulse generator, a transducer for transmitting acoustic waves in narrow beams, an acoustic pickup, a set of amplifiers, a delay timer, and an indicating display. The distance to an object depends on the echo delay. For sonar to be accurate, the speed of sound in the medium must be known. Precision sonar equipment can rival machine vision for mapping and navigation purposes. A high-level sonar set can differentiate among objects in its vicinity. This ability to distinguish individual objects, also called targets, from one another is called the resolution. In order for a sonar set to have high resolution, the acoustic-wave beam must be narrow, and it must be swept around in two or three dimensions