In Section IV of Liber XV, after the opening of the veil, we find the following rubric:
"The PRIESTESS is seated with the Paten in her right hand and the cup in her left."
In my annotated online version of Liber XV, I include the following note after that rubric:
[She then sets them down, the Paten to her left, the cup to her right.]
I have received a few questions about the rationale behind this note, so here is my painfully detailed explanation. Note--you'll want to have a copy of Liber XV open for reference before reading any further.
Firstly, in Section VIII, the rubric calls for the Priestess to clasp the Cup in her right hand, so the Cup must move from her left hand to her right hand at some point. The question, then, is--when does that switch occur?
When the Priest elevates the Host and Cup for the Trisagion at the end of Section VI, the rubric specifically calls for the Priest to take the Cup in his left hand and the Host in his right, implying that the Cup and Paten have switched positions before this point. But there are indications that the switch takes place earlier than this.
At the beginning of Section VI, the rubric calls for the Priest to make five crosses on the paten and cup: 1, 2, and 3 jointly on the paten and cup, 4 on the paten alone, and 5 on the cup alone. Now, we see later in Section VI that the Priest makes the five crosses on the Cup using the following pattern:

Presumably, this same pattern is applicable to all sets of five crosses made by the Priest in the ritual, e.g. on the Priestess after identifying the Covenant of Resurrection, and on the paten and cup at the beginning of Section VI. If so, then the paten and cup must have been switched before the five crosses are made on them at the beginning of Section VI, right after the Collects.
Now, it is possible for the Priestess to switch the positions of the paten and cup simply by crossing her arms at the end of Section IV and keeping them that way throughout Sections V, VI and VII, transferring the Cup to her right hand at the beginning of Section VIII when the Priest takes the Paten from her. This is not a completely unreasonable interpretation of the rubric--and it is, perhaps, the simplest interpretation of the rubric. However, I don't think it's a very practicable interpretation for universal application, because it requires the Priestess to take the Lance and hold it to her breast during the Collects while still holding both the Paten and cup. It is physically possible to do this by crossing the arms around the Lance, but this is an awkward and rather tricky maneuver that entails a non-negligible risk of either spilling the wine or dropping the Lance (which may be rather sharp), or both. Furthermore, the rubric simply states that the Priestess "holds [the Lance] to her breast." It does not state that she holds it to her breast "with her arms" or "with crossed arms," which is the sort of instruction one might expect if such an unusual method of "holding" were actually intended.
For the sake of safety, and simplicity and elegance of movement, we have the Priestess simply setting the implements down on the Altar surface before taking the Lance and holding it securely to her breast with her hands.
Assuming the Priestess does set the cup and Paten down at this point, the question arises as to when she picks them up again. The rubric does not specifically call for her to hold either implement again until Section VIII. However, there is a strong implication that the Priestess should pick up the Paten and Cup again at the beginning of Section VI. At that point, the rubric calls for the Priest to make three crosses jointly on the Paten and Cup before making one cross each on the Paten and Cup alone. It is difficult to imagine how this combination of crosses could be performed unless the Priestess were holding the Paten and cup in her hands. Therefore, we have included an annotation calling for the Priestess to pick up up the Cup and Paten at the very beginning of Section VI.
The only remaining question is whether the Priestess switches the Cup and Paten when she sets them down at the end of Section IV or when she picks them up again at the beginning of Section VI.
We chose the former (when she sets them down) for our practice, because it seemed less obtrusive at that point, and because it was, frankly, easier to remember that way.
93, 93/93
Sb