Analog Dial Interface, Digital Dial Interface (found on Acronym Finder)
The first way clocks can be classified is according to the style by which time is displayed to the reader, or the display type.
Analog
Perhaps the type of clock most people are familiar with are analog clocks. They use a clock face with numbers and hands to tell the time. The hands move around the clock face, indicating the hours and minutes. Aside from the popular 12-hour format, analog clocks can come in the 24-hour format, which is used to tell military time.
Digital
Digital clocks are also a popular type of clock display today. These clocks use two sets of numbers, separated by a colon to indicate the hour and minute. The time is projected using a display technology, such as LCD or LED. Early digital clocks had hard small plastic cards that would flip to the next number as time progressed. Most digital clocks are set for a 12-hour format, but some do come in a 24-hour format.