A clock or watch, or other time piece such as a chronograph or pulsometer, includes means for indicating the passage of time (or elapsed time). This indication may be audible but is most commonly visual and takes the form of a display. Known mechanical displays, hereto, include a dial with two or more hands rotatable about a co-axis on the dial such that the position of respective hands on the dial indicate the time. Known electrical displays include a liquid crystal display which is an alphanumeric display based on changes in reflectivity of a liquid crystal cell when an electric field is applied thereto.

It is desirable to provide a new display for displaying the passage of time.

Aspects of the invention are defined in the accompanying claims.

In order that the present invention may be well understood, an embodiment thereof, will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a display ; Figure 2 is a front view of the display of Figure 1; and

Figures 3 and 4 are schematic views of respective discs of the display of Figure 1.

Before describing the specific example shown in the drawings, the principle behind the display will be described more generally.

The display makes use of the alignment of respective radial lines extending on two or more co-axially aligned discs. Taking the example of two discs, the number of lines on each disc is different such that only one line of one of the discs can be perfectly, or angularly, aligned with any one of the lines of the other of the discs at a single point in time.

Rotation of the discs relative to each other causes the alignment of the lines of respective discs to rotate about the co-axis and when the discs are relatively rotated according to the passage of time, the alignment provides an indication of that time.

One or both of the discs may be partially transparent. By partially transparent, what is meant is that light is allowed to pass through the disc between the lines. If only one disc is partially transparent, light is allowed to pass through the outer disc, to reveal the alignment with the inner disc. The inner disc may be coloured or reflective to enhance the perception. Where both discs are transparent, light passing through both discs reveals the alignment.

More specifically, one disc may be provided with 30 equally circumferentially spaced radial lines while the other disc may be provided with one more or one less equally circumferentially spaced radial lines, ie 29

or 31 radial lines. The display would work with other numbers of lines, such as a number which is sufficiently numerous so that individual lines cannot easily be seen with the naked eye so that the alignment of lines is represented by graduated shading of the light.

Since there is one more line on one disc, than on the other disc, there can be alignment of one line of one disc with one line only of the other disc.

At a position diametrically opposed to the alignment, the lines of the two discs would be entirely misaligned. The alignment between these two extreme conditions circumferentially about the discs would change gradually between complete alignment, through partial alignment, to complete misalignment.

Hence, the amount of light able to pass through the discs would be different circumferentially about the discs. Likewise, if only one disc is partially transparent, the appearance of the inner disc would be different circumferentially about the discs.

When relative rotation of the discs takes place, the alignment (or the misalignment) is caused to rotate about the co-axis of the discs, and this property can be used to convey information. When relative rotation takes place according to the passage of time, the rotation of the alignment is an indicator of the passage of time and can be manipulated to display the passage of one or more time units (hours, minutes, etc) by reference to points or alphanumerics (eg 1 to 12) distributed circumferentially about the discs (like a prior art watch face described above). The angular speed of rotation of the alignment is proportional to, but much faster than, the angular speed of

relative rotation of the discs. The alignment, however, rotates in the opposite direction to the relative rotation of the discs. Although relative rotation of the discs causes the misalignment to rotate about the co-axis, it is desirable when displaying the passage of time for the misalignment to rotate clockwise. One way in which this can be achieved is described below.

A first disc is provided with n radial lines and a second disc is provided with n-1 radial lines (where n is an integer), the darkest part of the display (ie at complete misalignment) moves through an angle of 360 degrees for every relative rotation of the discs through 360/ (n-1) degrees. If the first disc with n radial lines is at the rear and the second disc with n-1 radial lines is at the front, then anti-clockwise rotation of the rear disc (the front disc being kept stationary) causes the misalignment to rotate clockwise about the co-axis. For the display of hours, the rear disc must be rotated relative to the front disc 360/ (n-1) degrees per twelve hours. For the display of minutes, the rear disc must be rotated 360/ (n-1) degrees per hour and for seconds, the rear discs must be rotated 360/(n-1) degrees per minute.

Using the above calculation, it is possible to select a rotational speed and number of lines to display hours, minutes and seconds. This can be achieved on a pair of discs per time unit, ie six discs in total for hours minutes and seconds. Also possible (as in the Figures) is a single disc paired with three other further discs making four discs in total. Alternatively, a greater number of lines (e. g. 349/348) can be provided at an outer radial region of one disc to display minutes and a lesser number of lines (e. g. 30/29) can be

provided at an inner radial region of another disc to display hours etc, without the need to rotate the regions at different angular speeds one from another.

The discs may both be rotated to achieve relative rotation, but more simply, one disc is fixed relative to the housing of the display device while the other disc is rotated, as described in the above example.

Referring now to the drawings, a display 10 is shown which comprises a disc 12 fixed relative to a housing (not shown) and a disc subdivided into three movable discs 14,16, 18. Discs 14 and 16 are annular in shape whereas disc 18 is circular. Discs 14,16, 18 are behind discs 12 as viewed in the direction of the arrow which is a typical viewing position for the display.

Discs 14,16, 18 are arranged on respective spindles 20,22, 24 for independent rotational movement relative to disc 12 about co-axis A of the discs 12, 14,16, 18. Means (not shown) are provided for causing rotation of disc 14,16, 18 in a predetermined manner so that the display is capable of displaying hours (disc 18), minutes (disc 16) and seconds (disc 14). The number of radial lines on the discs may be selected accordingly. In other words disc 12 may have a different number of radial lines at radially outer, radially inner and radially innermost regions to correspond with discs 14,16, 18. Alternatively, disc 12 may have the same number of radial lines at each radial region thereof, but discs 14, 16, 18 are rotated at different relative speeds to produce the desired effect.

Referring to Figures 3 and 4, an example of two discs 26,28 are shown for displaying the passage of a single unit of time. Both discs in this

example are partially transparent. The discs comprise a respective plurality of equally circumferentially spaced radially extending lines 30,32 divided by respective transparent portions 34,36. For clarity, only a relatively small number of lines are shown. In practice, it is desirable to provide a significantly greater number of lines. Since the number of lines shown is relatively small, the lines are represented by segments. With more lines present, the lines would be relatively more linear.

When one disc is placed over the other disc it will be seen that at angle 8 for both discs there is alignment of lines, whereas at angle a there is misalignment. Accordingly, light is allowed to pass through transparent portions proximate the line at angle 8 but not at those proximate the line at angle a. Relative rotation of the discs causes the light and dark regions of the discs to rotate about the co-axis A.

The housing or frame for the discs is preferably marked with indications of the hour as in a prior art watch or clock face. The time is indicated by the position of the dark portions of the discs as they rotate about the co-axis. Equally though, the time could be indicated by the position of the light portions.

In a modified example of a display, in which the basic arrangement is unchanged, discs 16 and 18 are fixed relative to each other or are integral.

The region of disc 16 which represents minutes has, say, 4320 radial lines whereas the region of disc 18 which represents hours has 360 radial lines.

With this relationship, the regions rotate about the co-axis at the same angular

speed to indicate both hours and minutes (ie the alignment of the outer region rotates at sixty times the angular speed of the inner region). The same principle could be used for the region of disc 14 (ie for seconds) but in practice the number of lines may become unfeasibly large to produce or the lines themselves may be too small to make the appearance clear enough to visualize. With this modified arrangement, the number of spindles required to drive the discs is reduced, enabling the production of a slimmer display.

Further, if the drive mechanism is mounted to one side of the display, rather than behind it, the practical limitation on the thickness of the time piece becomes the thickness of the drive mechanism and casing.

The display as described can be used as part of a clock, watch, chronograph, pulsometer, or any other device, or timepiece, for displaying time information.