The carriage clock, developed from designs associated with Abraham-Louis Breguet in the early nineteenth century, is defined by its architecture as much as its movement: a rectangular brass case with a carrying handle on top, glass panels on most or all sides (an 'anglaise' or similar case style) so the movement and platform escapement are visible, and a movement mounted on a separate platform above the going train, carrying a balance-and-spring escapement rather than a pendulum.
The platform escapement, almost always a lever escapement in later production, is what makes a carriage clock tolerant of being carried and set down at an angle or in motion, in contrast to a pendulum clock, which requires a stable vertical orientation to run at all. This is the same underlying design logic that makes any balance-and-spring timekeeper (a watch, a chronometer, a carriage clock) inherently more portable than a pendulum clock.
French carriage clocks of the later nineteenth century were produced in enormous variety of case style and complication — grande sonnerie and petite sonnerie striking, alarm, calendar and repeating variants are all recorded — and are generally identified by case style name, striking arrangement and the maker or retailer signature on the movement or dial, since many were retailed under a shop's name rather than the actual maker's.
Travel clocks in the broader, non-carriage sense include folding-case travel clocks, small desk clocks intended for luggage, and, in the twentieth century, compact clocks specifically marketed for travel with features such as shock-resistant mounting, luminous dials and, later, quartz movements; these are a looser and more heterogeneous category than the carriage clock proper, and the term should be used descriptively rather than as a precise type label unless the object matches carriage-clock convention specifically.
Deck watches and chronometer watches — large, robust watches carried aboard ship to compare against a fixed marine chronometer, or used as a portable timing reference — sit adjacent to this category functionally (both are portable precision timekeepers) but are watches rather than clocks by construction and are catalogued separately.
When cataloguing a carriage or travel clock, record the case style and material, the escapement type and whether a platform is fitted, the striking or repeating arrangement if any, and any maker's or retailer's signature on the movement, back plate or dial, since attribution in this category depends heavily on comparing case and movement details against published carriage-clock references rather than on a single obvious mark.