F.P Journe Octa Calendar Collection part 2

The five recesses around the cam's circumference, representing the four months of 30 days and February, act on the main lever that advances the date twice. At the end of April, June, September and November, the date-hand thus jumps from the 30th to the 1st. As it climbs out of the recess for February, which is deeper, the main lever moves the date three times, from February 29 to March 1.

It is only at the end of a February with 28 days, in three years out of four, that the date needs to be advanced manually. The date-hand rides up its scale on the curve of a snail cam mounted on the date-wheel. On the last day of the month, the date lever drops to the bottom of the cam, to bring the date-hand flying back to the start of its scale. The date-hand itself is mounted on the pinion between two racks, one of which incorporates a blade-spring.

The racks hold the date-hand precisely to the numeral on its scale, while controlling its return when the lever falls down the cam.