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Cyclos - a.m./p.m. or day & night


The idea for CYCLOS arose from the unsatisfying double meaning of the usual 12-hour scale. Every point on the scale designates both the day’s cycle and that of the night, without being able to differentiate between them. In the English speaking world one adds ‘ante meridiem’ or ‘post meridiem’ in order to make the distinction clear. The well known 24-hour clock, on which all the hours are ordered in one circle, has the disadvantage that one has to change ones perception of the angles of the hand in order to read the time.

In 1989 the architect and designer John C. Ermel, working on an order for a new watch design, had the idea of making the difference between the cycles of day and night obvious. This could be achieved by using a radially adjustable hour hand. He arranged the scale of hours on a so-called ‘Pascal’s spiral’, a conchoid of a circle, a special cycloid achieved by overlapping the usual clockwise rotation with translation in the radial direction – in this case a sine curve with a cycle of 24 hours.

The mechanism necessary for controlling such an hour hand took more than 10 years to develop and is a real marvel of Swiss watchmaking craftsmanship. In 1999 John C. Ermel applied for a Swiss patent on his idea, in 2000 for a worldwide patent. The first prototype of the CYCLOS watch was presented at the BASEL 2001 World Watch and Jewellery Show.

The 24-hour dual-phase watch combines the advantages of a classical analogue display with a clear differentiation between a.m./p.m. or the day and night cycles. This is achieved by dividing the double meaning of the usual 12-hour scale into two loops. A radially adjustable hour hand follows this curve and indicates thus all 24 hours clearly, although rotating with normal angular velocity.

The first production run watches have been delivered since summer 2003. The two collections available are based on two distinct design principles: the sporty "a.m./p.m." models in stainless steel cases or the elegant "day & night" models in gold cases, with dark or light dial each.

Exceptional is the elegant "Transparent Edition", which reveals the mechanical finesse of the unique dual-phase module by means of a partly transparent sapphire crystal dial.

Two designs depict, in different manner, the dual-track scale of these unique watches:

– on the sporty “a.m./p.m.” models, the hourly scale is formed by an outwardly winding spiral in red which indicates the hours “ante meridiem”, and an inwardly winding spiral in blue which indicates the hours “post meridiem”. The two phases are separated at 12 noon/midnight.

– on the elegant “day & night” models one sees an outer loop in gold which indicates the daytime hours, and an inner loop in white, silver or luminous which indicates the night time hours. Here, the two phases are separated from each other at 6h/18h.


Mechanical with automatic winding, ETA caliber 2892-A2, luxury finish (perlage, with blued screws), modified with the CYCLOS DualPhase module for controlling the length of the hour hand, certified COSC chronometer, CYCLOS logo engraved into the rotor (Geneva stripes)


Hours, by means of continual radial displacement of the hour hand on a dual-phase scale (Pascal’s spiral), minutes, center seconds hand, date at 6 o'clock


Black finish, color differentiation of the dual-phase hours scale ("a.m./p.m." or "day & night"), with a raised outer ring for distinction of the minute and second graduations, Superluminova luminescent numerals and hands 


Stainless Steel, Sapphire Crystal front and back


Diameter 39mm, Height 12.8mm


to 50m



For additional information please contact Partita +1(415) 447-0795

Cyclos - a.m./p.m. or day & night


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