These photos show some internal details of the grade 55, especially the lever-set mechanism under the dial.
The lever mechanism on this model has a circular wheel, with teeth on the inside, around the cannon pinion. This makes the teeth engage more smoothly, but the system lacks the natural torque to push the teeth against the cannon pinion when the wheel turns. These types often do not engage well to setting mode.
This example was made about 1868, in the first production run of the Elgin company.