The quintant allows the measurement of larger angles than the regular sextant. Larger angles are usefull when measuring horizontal angles as in hydrography or when doing a lunar distance measurement for time correction. Most quintants in my collection are surveying quintants and were used in hydrographic surveying. Those used in surveying usually have a handle for measuring horizontal rather than vertical angles. They also have additional legs for positining the instrument 'upside down' and they lack the filters used for making sun observatinos. Often they have a single filter on the telescope for reducing the overall light ('sunglasses' for the sextant).