Patent Publication Number: US-6711098-B2

Title: Device displaying calendar date

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to date display devices intended to be fitted to timepieces of the type including a movement and hands driven by the movement and displaying the time. 
     In the first watches of this type, the date was displayed by an additional hand making one revolution in 31 days. One of them, dating from the 18th century, is described at page 156 of the catalogue of selected works of the International Horological Museum in La Chaux-de-Fonds (ISBN 2-940088-07-1). It was thus an analogue type display. Such a solution is simple, but can only be read approximately, since the angle traveled by the hand each day is insufficient to allow two neighboring positions to be differentiated at a glance. 
     In most of the watches currently marketed, for example those shown at page 281 of the aforementioned catalogue, the display occurs in a digital manner, by means of a disc bearing the numbers from 1 to 31 and jumping forward each day. The date appears in a window made in the dial. The figures displaying this information have to be of small dimensions, and are thus difficult to read. 
     One solution to this problem consists in providing the device with first and second display members mounted so as to move in rotation on the movement, arranged under a dial provided with apertures. These members are respectively intended to display the units and the tens of the date by means of figures, visible through the apertures. The device further includes a drive and positioning mechanism controlled by the movement and arranged so as to cause one or the other or both of the members to jump forward once a day. 
     Such a device is, for example, disclosed in Swiss Patent No. 310 559. This device is controlled by a clockwork movement, by means of a wheel making a revolution in 24 hours. The latter drives through 1/31st of a revolution, and once a day, a wheel assembly including two superposed wheels. The display members are formed of two discs arranged side by side, one displaying the tens of the date and the other the units, the current date appearing in an aperture of the dial. 
     The wheel assembly and the discs are arranged so that, when the units figure of the date displayed is equal to 0 or comprised between 2 and 8, only the units disc is driven, when the units figure is equal to 9, the units and the tens discs are both driven, when the units figure is equal to 1 and the tens figure to 0, 1 or 2, only the units disc is driven, and when the units figure is equal to 1 and the tens figure to 3, only the tens disc is driven. Such a device allows the date to be displayed by means of figures of large dimensions. 
     It is evident that the date is easier to read, but less aesthetically pleasing, the more apparent it is, since the figures overload the dial. 
     Another solution is disclosed in European Patent No. 0 619 035. It relates to an electronic watch of the analogue type, wherein the date is displayed by means of two hands. The first indicates the tens, in four positions making an angle of 90° between them, while the second displays the units, in ten positions regularly distributed over one revolution. 
     This solution can only be envisaged insofar as figures are located facing the position of the hands. This is necessary to permit reading, since the hands do not occupy a usual position for a given value, as is the case of the hour and minute display. This solution thus loads the dial considerably, without however making it simple to read. 
     The object of the present invention is to allow a display of the date in a particularly readable manner while contributing to the aesthetic appearance of the timepiece. 
     SUMMARY OF THE INVENTION 
     Therefore, the display device according to the invention, which is intended to be fitted to a timepiece of the type including a movement, a dial and hands, the latter being driven by the movement and displaying the time, includes first and second display members, driven in rotation by the movement, intended to display respectively the units and the tens of the date, and a drive and positioning mechanism controlled by the movement and arranged so as to cause one or the other or both of the display members to jump forward once a day. It is characterized in that the first member is mounted on the movement, pivoting about an axis which is perpendicular thereto and bears an index, and in that the mechanism and the first member are arranged so that, when the mechanism causes the display of the units of the date to pass from a value n to n+1, n being an integer number comprised between 1 and 9, the first member travels, in the clockwise direction, through an angle equal to 30°, and in that, when n is equal to 1, the index is located in a position corresponding to the position which an hour hand, pivoting about the axis of the first member, would occupy, when it is one o&#39;clock. 
     In order to assure the passage from 9 to 0, the mechanism and the first member are arranged so that the latter performs a jump of 90° when n is equal to 0, so that the index passes from the &lt;&lt;nine o&#39;clock&gt;&gt; position to the &lt;&lt;midday&gt;&gt; position, via the shortest route. 
     In a particularly advantageous embodiment, the first member is formed of a disc, bearing the index, and placed underneath the dial. The latter includes nine apertures disposed in an arc of a circle substantially concentric with the disc, the first aperture occupying a position corresponding to &lt;&lt;1 o&#39;clock&gt;&gt; and the following ones making an angle of 30° with respect to each other, with reference to the central point of the arc of the circle, so that the last aperture is located in the &lt;&lt;9 o&#39;clock&gt;&gt; position, so that altogether the index of the first member is visible through the apertures. 
     If, in order to display the units, it seems advantageous to use an index whose position corresponds to that of an hour hand, the situation is different for the indication of the tens. Indeed, perception of a number of objects comprised between 0 and 3 occurs without any problem and at first glance. This is why, advantageously, the second display member is also formed of a disc mounted so as to pivot on the movement and which bears three indices disposed in an arc of a circle, and the dial includes three apertures which are also disposed in an arc of a circle and of the same radius as the arc formed by the indices. Further, the tens display member and the drive and positioning mechanism are arranged so that zero, one, two or the three indices are visible through the three apertures, depending upon whether the figure of the tens is equal to 0, 1, 2 or 3. 
     An aesthetically pleasing display requires precise positioning of the discs. This is why it is advantageous for the mechanism to include two star wheels with twelve teeth, respectively secured to the first and second members and each cooperating with a jumper spring to position it. 
     In order to permit an optimum drive which only requires a correction for the months of less than 31 days, the mechanism and the display members are arranged so that, when the units figure of the date is equal to 0 or comprised between 2 and 8, only the units disc is driven, when the units figure is equal to 9, the units and tens discs are both driven, when the units figure is equal to 1, and the tens figure to 0, 1 or 2, only the units disc is driven, and when the units figure is equal to 1 and the tens figure to 3, only the tens disc is driven. 
     In order to assure optimum driving of the device, the mechanism further includes: 
     a &lt;&lt;24 hour&gt;&gt; wheel, completing one revolution per day, driven by said movement, and carrying a drive finger, 
     a lever, mounted so as to pivot on the movement, actuated by said drive finger and cooperating with a return spring, provided with first, second, third and fourth drive means and positioning means, the first drive means cooperating with the star wheel with twelve teeth secured to the first member and causing it to move forward by one step each day, 
     a date wheel assembly including a date star-wheel, with 31 teeth, making one step per day via the action of second drive means, and a day cam, cooperating with the lever positioning means and defining three levels, the first, upper, level, corresponding to the position occupied by the date wheel assembly on the 31st of the month, the second, median, level corresponding to the positions occupied by the date wheel assembly when the units figure of the date is equal to zero, or comprised between 2 and 8, or when the units figure is equal to 1 and the tens figure to 0, 1 or 2, and the third, lower, level, corresponding to the position occupied by the date wheel assembly when the units figure is equal to 9, 
     a drive flirt for the star wheel with twelve teeth secured to the second member, provided with a star wheel with ten teeth and driven through one step per day by the third drive means of the lever, with the exception of the day when the positioning means abut against the upper level of the cam, and arranged so that the flirt is released when the units figure of the date is equal to 9, 
     a retrograde unit for the tens including a star wheel with 31 teeth, kinematically connected to the star wheel with 31 teeth of the date wheel assembly, released when the lever positioning means abut against the upper level of said cam, 
     a return spring of the second member, wound each time that the drive flirt moves the second member forward and let down when the retrograde unit is released, and 
     a drive lever, secured in rotation to the first member and cooperating with the fourth drive means, to cause the star wheel with twelve teeth secured to the first member to move forward three steps each time that the lever positioning means abut against the lower level of the cam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will appear from the following description, made with reference to the annexed drawing, in which: 
     FIGS. 1 and 2 show two alternative arrangements of the display members; 
     FIGS. 3 and 4 show the drive mechanism for a display of the 29th of the month, certain parts having been removed in FIG. 4, to facilitate comprehension of the invention, and 
     FIGS. 5 and 6 are respectively plan and cross-sectional views of a part of this mechanism. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The watches, shown schematically in FIGS. 1 and 2, include, in a conventional manner, a dial  10  and, placed in front of this dial, hands  12  and  14  respectively displaying the hours and the minutes. 
     In FIG. 1, the watch is barrel-shaped. Its dial carries an hour-circle  16  formed of numbers from 1 to 12, except 6. It is also provided with a set of nine apertures  20  intended to display the units of the date, and a set of three apertures  22  for the display of the tens of the date, respectively disposed on two concentric circles occupying the space comprised between the center and the 6 o&#39;clock position of the dial. 
     In this watch, the date display is achieved by means of an index  24 , intended to indicate the value of the units figure by its position and three indices  26 , intended to display the tens figure, the latter being equal to the number of indices visible. 
     The apertures  20  define between them an angle of 30°, namely the angle which the hour hand travels in an hour. In other words, if an hour hand pivoted at the center of the concentric circles, it would be located, facing aperture  20   a  at 1 o&#39;clock, second aperture  20   b  at 2 o&#39;clock etc. 
     Index  24  appears through one of apertures  20  and indicates the units figure of the date by its position, the latter being equal to 3 in FIG.  1 . Two of indices  26  are visible through the first two apertures  22   a  and  22   b , to indicate that the tens figure is equal to 2. In other words, the current date is equal to 23. 
     In the embodiment of FIG. 2, apertures  20  are located facing the FIGS. 1 to  9  of hour circle  16 , aperture  20   f , next to the FIG. 6, framing index  24 . The units figure is thus equal to 6. 
     Apertures  22  are arranged in the zone comprised between 11 o&#39;clock and 1 o&#39;clock, two indices  26  appearing in apertures  22   a  and  22   b . The tens figure is thus equal to 2. In this case, the date displayed is thus equal to 26. 
     In the two examples described above, cut out portions  20  and  22  are round. It is evident that they may have other shapes. Thus, in the case of the example of FIG. 2, these apertures could also, advantageously, have the shape of the figure corresponding to its position and thus replace hour circle  16 . 
     FIGS. 3 and 4 show a watch movement, displaying the date according to the embodiment of FIG. 1, the components of which occupy their position corresponding to the 29th of the month. These Figures differ in the masking or removal of all or part of certain parts. 
     The movement includes a plate  28  on which a drive mechanism  30  is mounted and concentric discs  32  and  34 , shown in a dotted line in FIG.  3  and bearing respectively index  24  and the three indices  26 , which are not shown in this Figure. 
     The watch movement further includes a time base and a gear train, which are not visible in the drawing, since they are located on the other side of plate  28 , with the exception of hour wheel  36  disposed at the center of the movement and intended to carry hour hand  12 . 
     Mechanism  30  is connected to hour wheel  36  by a &lt;&lt;24 hour&gt;&gt; wheel  38 , completing one revolution per day, and mounted so as to pivot on plate  28 , on a stud which is not visible in the drawing, and held axially by means of a screw  40 . A finger  42 , coaxial with wheel  38 , is secured, in rotation, to wheel  38 , by a pin  38   a  driven into the plate of wheel  38  and abutting against finger  42 . 
     Mechanism  30  includes, distributed over the periphery of the plate and considered in the clockwise direction, from the &lt;&lt;midday&gt;&gt; position, a lever  44  mounted so as to pivot and secured in proximity to &lt;&lt;midday&gt;&gt; by means of a screw  46 , a date wheel assembly  48  disposed in proximity to &lt;&lt;3 o&#39;clock&gt;&gt;, a retrograde tens unit  50  placed in proximity to &lt;&lt;4 o&#39;clock&gt;&gt;, a units wheel assembly  54  and a tens wheel assembly  56 , coaxial and located at &lt;&lt;6 o&#39;clock&gt;&gt;, and a tens unit  52 , which is located in proximity to &lt;&lt;8 o&#39;clock&gt;&gt;. 
     More precisely, lever  44  includes a bulge  44   a  pierced by a hole in which screw  46  is engaged. It is formed of first and second arms  44   b  and  44   c , disposed on either side of bulge  44   a . Arm  44   b  forms, at its free end, a finger  44   d  intended to cooperate with unit  52 . 
     Second arm  44   c  is provided with a fork with two teeth  44   e  and  44   f . Tooth  44   e  ends in a finger  44   g  intended to cooperate with wheel assembly  48 . Tooth  44   f  includes, in its median part, a snug  44   h  intended to cooperate with date wheel assembly  48 . It forms, at its free end, a finger  44   i  intended to cooperate with units wheel  54  and further carries a drive lever  58 . The latter is mounted so as to pivot by means of a screw  60  and is provided with a spring  58   a  abutting against a pin  62  disposed on tooth  44   f . Spring  58   a  generates a force intended to apply lever  58  against units wheel set  54 , as will be specified hereinbelow. 
     Lever  44  has to be held in place so that it remains in a plane perpendicular to the pivoting axis. Therefore, arm  44   b  includes a cut out portion  44   k , in an arc of a circle, the center of which coincides with the axis of screw  46 ; a screw  64  with a shoulder is engaged therein and limits axial movements. 
     A lever spring  66 , secured by means of a screw  67  on the periphery of the plate, in proximity to &lt;&lt;1 o&#39;clock&gt;&gt;, cooperates with a pin  68  secured to tooth  44   f  and generates a torque tending to cause lever  44  to rotate in the clockwise direction. The latter is thus held in the rest position, as seen in FIGS. 3 and 4, finger  44   g  abutting against date wheel assembly  48 . 
     Date wheel assembly  48  includes, superposed, a star wheel with 31 teeth  70  and a cam  72 , secured to each other in rotation. It pivots on a stud of plate  28 , which is not visible in the drawing, on which it is held axially by means of a screw  74 . Star wheel  70  is provided with a toothing of triangular profile, disposed in the same plane as snug  44   h  and on its path, so that, each day at midnight, this snug causes wheel assembly  48  to move forward by one step. The latter thus makes one revolution per month. A jumper spring  76 , secured by means of a screw  78  to the periphery of plate  28 , in proximity to &lt;&lt;2 o&#39;clock&gt;&gt;, cooperates with the toothing of star wheel  70  to position wheel assembly  48 . 
     Cam  72  has three radial levels, with three cut out portions or notches  72   a ,  72   b  and  72   c  defining a lower level, corresponding to the passages of the date to a higher ten, a protrusion  72   d  defining an upper level and corresponding to the passage from the 31st to the 1st of the month, and four surfaces in a portion of a circle  72   e  to  72   h , disposed between the notches and the protrusion and defining an intermediate level, corresponding to the other days of the date. It is located at the same level as finger  44   g  and acts as a support for lever  44  in the rest position. 
     Retrograde tens unit  50  includes a star wheel with 31 teeth  80  provided with a toothing of triangular profile meshed with the toothing of star wheel  70 , and a cam  82  disposed above star wheel  80 . Like wheel assembly  48 , it completes one revolution per month. It pivots on a stud of plate  28 , which is not visible in the drawing, on which it is held axially by means of a screw  84  defining its pivoting axis. 
     Cam  82  is formed of a snail shaped part  86  and a finger  88  which are superposed and secured to each other in rotation. Snail shaped part  86  includes a circular cut out portion  90 , in which a pin  92 , secured to star wheel  80 , is engaged. Pin  92  assures the connection between star wheel  80  and cam  82 , so that, each time that star wheel  80  moves forward, it drives with it cam  82 . Because of cut out portion  90 , in which pin  92  is engaged, finger  88  and snail shaped part  86  can have a relative movement of approximately  450 . 
     Retrograde tens unit  50  cooperates with a jumper spring  94  and a flirt  95 , respectively secured by means of screws  96  and  97 , between &lt;&lt;5 o&#39;clock&gt;&gt; and &lt;&lt;6 o&#39;clock&gt;&gt;. Jumper spring  94  is engaged in the toothing of star wheel  80 , to position it. Flirt  95  abuts against snail shaped part  86 , to control the backward movement of the tens as will be explained hereinbelow. 
     Tens unit  52  includes a star wheel with ten teeth  98  and a cam  100 . Star wheel  98  includes a triangular toothing disposed at the same height as finger  44   d  with which it cooperates, so as to cause it to move forward by one step each day. It thus completes one revolution in ten days. Unit  52  is mounted so as to pivot on a stud of plate  28 , which is not visible in the drawing, on which it is held axially by means of a screw  102 . 
     Cam  100  is formed of a snail shaped part  104  and a finger  106  which are superposed and secured to each other in rotation. Star wheel  98  includes a circular cut out portion  108 , in which a pin  110 , secured to snail shaped part  104 , is engaged. Pin  110  assures the connection between star wheel  98  and cam  100 , so that, each time that star wheel  98  moves forward, it drives with it cam  100 . Because of cut out portion  108 , in which pin  110  is engaged, finger  106  and snail shaped part  104  can have a relative movement of approximately 45°. 
     Tens Unit  52  cooperates with a jumper spring  112  and a flirt  113 , secured respectively to the periphery of the plate, in proximity to &lt;&lt;7 o&#39;clock&gt;&gt;, by means of screws  114  and  115 . Jumper spring  112  is engaged in the toothing of star wheel  98  and intended to position it. Flirt  113  abuts against snail shaped part  104  to control the jumping forward of the tens, as will be explained hereinbelow. 
     FIGS. 5 and 6 show, in detail, wheel assemblies  54  and  56 , as well as, in FIG. 6 only, discs  32  and  34  which are respectively associated therewith. More precisely, FIG. 5 is a top view and FIG. 6 a cross-section along the line VI—VI of FIG.  5 . 
     As can be see in these Figures, wheel assemblies  54  and  56  are coaxial, mounted so as to pivot on a stud  116  driven into plate  28 . They are arranged so that they can rotate freely with respect to each other. 
     More precisely, units wheel assembly  54  includes a star wheel with twelve teeth  118  and a snail shaped part  120 , which are superposed and connected to each other and to the units disc  32 , disposed above snail shaped part  120 , by means of two screw studs  122 . 
     Star wheel  118  includes a toothing of triangular profile disposed in the same plane as finger  44   i  and on its path, so as to be driven by one step per day. 
     Snail shaped part  120  is located in the same plane as drive lever  58 , with which it cooperates at the end of each day whose date ends in &lt;&lt;9&gt;&gt;, as will be explained hereinbelow. 
     Star wheel  118 , snail shaped part  120  and disc  32  are pierced with central circular holes of the same diameter, which together form a bearing  123 . 
     Tens wheel assembly  56 , which carries disc  34 , is formed of a pipe  124 , mounted so as to pivot on stud  116 , a star wheel with twelve teeth  126 , of triangular profile, riveted onto pipe  124 , and a rack  127 , secured in rotation to star wheel  126 . 
     In order to assure the securing thereof to pipe  124 , disc  34  includes, on its bottom face, a socket  34   a  engaged in bearing  123 . 
     Pipe  124  includes three cylindrical portions  124   a ,  124   b  and  124   c . Portion  124   a , adjacent to plate  28 , carries star wheel  126 . Portion  124   b , which is intermediate and of larger diameter acts as a pivot for bearing  123 . It is of the same diameter as socket  34   a . Finally, portion  124   c  is driven into socket  34   a , to secure disc  34  and wheel assembly  56  rigidly to each other, the assembly formed by disc  32  and wheel assembly  54  being imprisoned therein. 
     As FIG. 4 shows, a spring  128  and jumper spring  129  cooperate with wheel assembly  56 . They are respectively secured to the periphery of the plate by means of screws  130  and  131 , spring  128  in proximity to &lt;&lt;4 o&#39;clock&gt;&gt;, jumper spring  129  in proximity to &lt;&lt;7 o&#39;clock&gt;&gt;. Star wheel  126  carries a pin  132 , disposed at the same height as spring  128  and abutting against its end  128   a.    
     A pin  134 , driven into plate  28 , acts as a stop for rack  127  when the latter reaches the end of its travel. 
     Jumper spring  129  is engaged in the toothing of star wheel  126 . It is extended by a stem  129   a  which is located in the space swept by finger  88 . 
     In order to understand how wheel assembly  54  is positioned, reference must be made to FIG. 3, which shows a jumper spring  136  meshed with the toothing of star wheel  118 . Jumper spring  136  is secured to plate  28  by means of a screw  138  disposed in proximity to 6 o&#39;clock. 
     In the preceding description, the different jumper springs and flirts have been described as being secured to the plate by means of screws. It goes without saying that, to guarantee precise positioning, it is advantageous to arrange pins in the plate and to provide each of the jumper springs and flirts with holes in which the pins engage. This method is well known to those skilled in the art, which is why it has not been shown, to avoid overloading the drawing. 
     Mechanism  30 , as it has just been described, includes three operating sequences, defined by the initial position of lever  44 , abutting against cam  72 . 
     Every day, with the exception of the 9th, 19th, 29th and 31st of the month, finger  44   g  of lever  44  rests on the median level of the cam, defined by sectors  72   e  to  72   h . On the 9th, 19th and 29th, it is engaged respectively in notches  72   a ,  72   b  and  72   c . Finally, on the 31st, finger  44   g  abuts against protrusion  72   d . These different situations will be examined in succession hereinbelow. 
     For more than twenty hours, &lt;&lt;24 hour&gt;&gt; wheel  38  rotates freely, driving finger  42 , via pin  38   a . During this time, lever  44  is in the rest position, defined by finger  44   g  abutting against cam  72 . Mechanism  30  is then stationary. 
     Around 22 hours, finger  42  comes into contact with lever  44 , abutting in the forking zone of arm  44   c , and more particularly against the wall of tooth  44   f . The lever then pivots slowly at  44   a , in the anti-clockwise direction, winding spring  66 , such that it exerts a counter-reaction force on finger  42 . 
     When finger  44   g  abuts against the median portion of cam  72 , and just before the counter-reaction force passes through the axis of screw  40 , fingers  44   d ,  44   i  and snug  44   h  respectively come into contact with the toothings of star wheels  70 ,  98  and  118 , making all three move forward one step. 
     Since disc  32  is secured in rotation to star wheel  118 , index  24 , carried by disc  32  consequently passes from one aperture  20  to the other by one step per day, until it reaches aperture  20   i , located at 9 o&#39;clock, which indicates that the units of the date are equal to 9. 
     After the counter-reaction force has passed the axis of screw  40 , it generates a torque on finger  42  tending to move it away from pin  38   a . Lever  44  then pivots in the clockwise direction, driven by the force exerted by spring  66 , until finger  44   g  comes into contact with cam  72  again. If the date of the next day is different from 9, 19, 29 or 31, the finger comes to abut in the median portion of cam  72 . Consequently, some 20 hours later, the same chain of events reoccurs. 
     If, conversely, the units figure of the date of the next day is equal to 9, finger  44   g  then engages in one of bottom notches  72   a ,  72   b  or  72   c . Moreover, units wheel assembly  54  has rotated so that drive lever  58  is caught on the connection plane  120   a  of the two ends of the spiral of snail shaped part  120 . 
     When finger  42  comes into contact with lever  44  located in this position, its movement begins by making wheel assembly  54  rotate, successively through three times 30°, so that units index  24  is located in the midday position of the dial. Since the latter does not include an aperture at this location, the index is thus masked, thereby indicating that the units figure is equal to 0. 
     Further, as previously explained, snug  44   h  drives the toothing of star wheel  70 , while finger  44   d  causes the toothing of star wheel  98  also to move forward by one step and, with it, cam  100 . 
     The latter is disposed so that flirt  113  then passes the outer end of snail shaped part  104  and causes the abrupt displacement of cam  100 , so that finger  106  drives a tooth of rack  127 . Tens wheel assembly  56  thus moves forward by one step and an additional index  26  is visible through tens apertures  22 . 
     After the counter-reaction force has passed the axis of screw  40 , lever  44  fall again and abuts a median portion of cam  72 . The next day, the operation thus corresponds to what was previously described, the index reappearing in aperture  20   a  to indicate that the units figure is equal to 1. 
     During the passage from the 31st to the first of the following month, units disc  32  and tens unit  52  must remain in the positions which they occupy and the tens disc must move backwards so that tens indices  26  disappear. 
     These conditions are satisfied owing to the fact that the amplitude of the movement of lever  44  is reduced, finger  44   g  abutting against protrusion  72   d . Consequently, the movement of fingers  44   d  and  44   i  is insufficient to drive the toothings of star wheels  98  and  118 . In other words, only snug  44   h  works normally, and causes the toothing of star wheel  70  to jump forward by one step. This toothing drives with it star wheel  80  and snail shaped part  86 , which reaches a position such that flirt  95  passes the top end of snail shaped part  86 . 
     This results in a torque which causes an abrupt rotation of snail shaped part  86  and finger  88 . The latter raises stem  129   a . Jumper spring  129  is then released from star wheel  126 . Spring  128  is no longer held, so that it causes star wheel  126  to rotate in the anti-clockwise direction, over an angle of 90°. In this position, the three indices  22  are masked by the dial, the tens figure of the date being thus equal to zero. 
     The device according to the invention may, of course, be the subject of numerous variants. It is possible in particular to associate therewith a rapid correction mechanism, controlled in a conventional manner by a time-setting stem. 
     It is also possible to associate therewith control means of the type fitted to perpetual calendar watches. In this case, the month could be indicated by another index, advantageously less apparent than the index of the first member, moving facing the hour circle. Consequently, this other index would face the 1 in January, the 2 in February, etc.