Montblanc has become a real watch manufacturer in the meantime. With more and more in-house movements the brand satisfies more and more customers. I personally like this years calibre MB R220 used for the Rieussec Rising Hours.

When observing the evolution of Montblanc’s Nicolas Rieussec chronographs, one might be tempted to conclude that time is a disc. Montblanc first used rotating discs to replace the hands on the chronograph’s counters for sixty elapsed seconds and thirty elapsed minutes. A rotating disc was afterwards installed to indicate the hour in a second time zone. And now the manufacture debuts its Nicolas Rieussec Rising Hours, which relies on two discs, one atop the other, to show not only the twelve hours, but to also indicate whether each of the dozen is a daytime or night-time hour.

Alexander told me: “We have built a day/night indication into the hour display. A digital hour display wouldn’t have been anything new per se.”

Instead of an hour-hand, there is a circular aperture at the “12” in which a disc bearing Arabic numerals for the twelve hours turns below a little triangular index. Aficionados will no doubt have seen similar digital hour displays on other timepieces in the past, but the Nicolas Rieussec Rising Hours goes one decisive step further: its hour numerals change colour depending on the time of day or night. The numerals are pale blue during nighttime hours and black during the day.

This unusual time display is made possible by the new manufacture calibre MB R220, which boasts an mechanism consisting of two rotating discs positioned one atop the other. The Arabic numerals 1 to 12 are cut from the upper disc. This twelve-hour disc turns above the bicolour day/night disc, which is half pastel blue and half black so that a light or dark hue appears in the skeletonised numeral in the window depending on the time of day or night. The twelve-hour disc rotates continually, while the day/night disc turns in intervals and at variable speeds to produce the desired colour change (pale blue for the night, black for the day) in the cut-out numerals. This complex motion is controlled with the aid of a Maltese cross mechanism consisting of two cam-like wheels. One of these cams is mounted on the propelling staff of the day/night disc; the other is affixed to an extension of the hour-staff.

What you see here is huge demo model made out of plastic and of course NOT any part belonging to the real watch!

Each cam’s profile is specially shaped so that the cams turn idly past one another between 9 a.m. and 3 p.m. (and again between 9 p.m. and 3 a.m.); the day/night disc is accordingly motionless throughout both these intervals. Meshing begins at 3 a.m. (and 3 p.m.). This engagement causes the day/night disc to turn at an increasingly faster pace until two teeth on either side engage in a way that the day/night disc no longer accelerates but instead continues to turn synchronously with the twelve-hour disc – this occurs from 4:30 a.m. to 7:30 a.m. (and from 4:30 p.m. to 7:30 p.m.). Afterwards, the day/night disc decelerates between 7:30 a.m. and 9 a.m. (and between 7:30 p.m. and 9 p.m.) until the meshing is completely separated, whereupon the day/night disc comes to a standstill.

This patented “Rising Hours” mechanism is particularly self-explanatory twice a day: at six o’clock each morning, the pierced digit “6” appears light blue on the left and black on the right to symbolize that night is ending and day is dawning; at six o’clock each evening, black daylight at the left yields to pastel blue night-time hours at the right.