It is the fabricate of the prosthesis of the incisal teeth of the up and down jaw.

Mark the cusp of the model of the upper jaw in the occlusion rim in the dentate Arch.

As for 123mm being written to the occlusion rim in the dentate arch, it is the distance of even the incisal tooth from the arbitrary hinge axis point.

It adapts the occlusion rim in the Dentate arch in the mouth.
Adjust a front view with the occlusal plane plate to intersect vertically in the median-sadittal-plane, and, adjust a lateral view to become parallel in the Camper's line.

As for this adjustment, the dentist confirms whether it intersects vertically in the median-sadittal-plane, quoting a line in the plastic sheet, and put it to the patient's face.
A human eye is very unreliable.
If there is this plastic sheet, it can be confirmed in the considerable precision.

Measure a distance to the the incisal angle of the incisal tooth from the arbitrary hinge axis point, it is transfered in the Articulator.
By transfering this distance in the Articulator, a position is settled before and after the model.
Then, by mounting by using the occlusion rim in the dentate Arch, the median line of the model and the inclination of the right and left is decided.
It becomes only related to the up-down position that it more becomes a problem.
But, if a bite taking occurs by the vertical demension which one wants to give to it, it doesn't need to change a vertical demension on the Articulator any more with incisal pin.

Therefore, don't you think this error that it can be held to a minimum?