In a watch, as in this compteur, the dome is a double back cover with holes through which can be seen the shaft squares used to wind the springs and set the hands to the correct time. The holes in the compteur's dome are shown in figures 53 and 54.
We can see:
1) Through the largest opening, we can see the power reserve index (as described earlier in the 'Power reserve' section). However, there are no markings other than the lines of dots, the meaning of which remains a mystery (see close-up in figure 53a).
Fig.53 and Fig.53a
Fig. 54 and Fig.56
2) Here we have an oblong opening, through which can be seen a small triangle against a blued background (in the close-up in figure 56, the opening is indicated by the dotted lines). This offers the option of changing the period by moving the index over the balance-cock. The blued plate serves as a dustproof band and the index can be moved by inserting a pointed object into the small hole around the triangle. Surprisingly, the letters 'A' and 'R', which are normally included, are nowhere to be seen.
3) This is the fusee shaft square, into which the user can insert a key to wind the spring.
4) This is the barrel shaft square for the original winding ratchet. This hole serves no purpose as the shaft is used only by the watchmaker when the watch is being made.
5) The 2 openings indicated by the number 5 reveal a specific feature that once again demonstrates Louis Moinet's professionalism and deserves an explanation.
Normally, the dome is mounted on a hinge, indeed, and is sometimes even simply forced. It always has a lip that allows it to be opened or removed. However, this compteur has nothing of the kind and it is here that Louis Moinet showed real ingenuity. Doubtless this was to ensure that no one could open up his compteur, which it appears he made (or had made) primarily for his own personal use. Presumably he wished to keep his invention a secret. To this end, he made an unusual fastening mechanism that made opening the dome particularly difficult for anyone unfamiliar with this mechanism, as shown below:
The movement, fitted in its case, is shown in figure 57. There are two openings at the edge of the movement, shown by the arrows. The dome (Fig. 58) holds 2 screws (see arrows), the heads of which project and are inserted into the openings on the movement but slide under the middle of the case. The part highlighted by the red oval in figure 57 is shown in greater detail in figure 59.
A part with 2 holes on the top and a notch on the bottom (figures 60 and 60a, top and bottom respectively) is inserted into the hole, where it can turn (figure 61). A pierced post (shown in figures 59 and 61) is fitted onto a blade that springs back. The end of the post is semicircular and has a fingerpiece (blade only shown in figure 63).
Without going into further detail, it is simply important to understand that when everything is in place, the parts work together to lock the dome. The 2 small holes for the part in figure 60 and a screw inside the post can be seen through the holes in the dome, as shown in figure 62.
To remove the dome, you need to remove the screw from the post, then simultaneously press down on the post while turning the part with a special tool (figure 64). Once the notch is in line with the fingerpiece, the dome can be removed
Un pièce avec sur le dessus 2 trous, et à sa base une encoche (Fig. 60 et 60a dessus et dessous), se positionne dans le trou dans lequel elle peut tourner (Fig. 61).