Mechanisms for mapping between locators, names, and descriptive identifiers. Anti-theft systems include devices such as locks and keys, RFID tags, and GPS locators. Internet resource locators, described in RFC 1736, convey location and access information for resources. Port numbers are sometimes seen in web or other uniform resource locators (URLs). Z characters are used for address locators, product types, and customer and service information. On the VHF/UHF bands, many radio amateurs pursue awards based on Maidenhead grid locators. During the 1970s, the long-range mobile UHF 5H87 and SHF 5H69 low-altitude locators were used. Biddle was one of the first companies to provide commercial cable fault locators. Its aim is to provide facilities that will cater to light and medium sized locators. An early (1993) draft of the HTML Specification referred to "Universal" Resource Locators. The original electronic apex locators operated on the direct current principle. This was followed by the Vehicle Locators and Marketing Network sales toolsets. The US Army also used sound locators. Subic sees roughly 1 cargo ship per week, and has many licensed locators. Thus, when the pagination is changed the index can be regenerated with the new locators.