ὑπολογισμός (composed of ὑπολογισμός, hora, time, hour, and λόγος, speech, discourse), a common name amongst ancient writers for any instrument or machine for measuring the hours. (See Chronometer.)

Modern inventions and gradual improvements have given birth to some new terms, and annexed meanings to others totally different from those which they originally had. All chronometers which announced the hour by striking on a bell were called clocks. Thus we read of pocket-clocks, though nothing would seem more absurd than to suppose that a clock, according to the modern idea, should be carried in the pocket. In like manner, all clocks which did not strike the hour were called watches or time-pieces; and the different parts of a striking clock were distinguished by the watch part and the clock part; the former meaning that part which measures the time, and the latter the part which proclaims the hours. In the report of Sir Isaac Newton to the House of Commons in 1719, relative to the longitude act, he states the difficulties of ascertaining the longitude by means of a watch; yet it is obvious, from several circumstances, that his remarks were directly to be understood of a time-piece, regulated by a pendulum; for his objections are founded on the known properties of the pendulum, some of which differ essentially from the properties of the balance and spring. It is also to be remembered that all the attempts of Huygens for finding the longitude were by means of pendulum clocks which did not strike the hour, and which consequently, according to the language of the times, were called watches. At this time such machines for measuring time as were fixed in one place were called clocks if they struck the hour; if they did not strike the hour, they were called time-pieces; and when constructed with greater care, for a more accurate measure of time, they were called regulators. Some artists have affected to call such watches as were constructed for astronomical and nautical observations by the name of

time-pieces, probably to intimate that they possess the advantages of those constructed with a pendulum.