Regarding voting, clause 3 of the same section provides in part that "the Yeas and Nays of the Members of either House on any question shall, at the Desire of one fifth of those present, be entered on the Journal." As a regular practice, however, the Senate presumes that it is complying with the Constitution. Therefore, it presumes that a quorum always is present unless and until the absence of a quorum is suggested or demonstrated:
The Senate operates on the presumption that a quorum is present at all times, under all circumstances, unless the question to the contrary is raised, or the absence of a quorum is officially shown, or until a point of no quorum is made even though a voice vote is taken and announced in the meantime. Under the Senate's standing rules, if no other Senator has the floor, any Senator (including a Senator who is presiding) may "suggest the absence of a quorum." Once the quorum call has begun, the Senate may not resume the conduct of business until a majority of Senators respond to this call, or unless the Senate agrees by unanimous consent to "dispense with further proceedings under the quorum call." Because most quorum calls are intended to suspend the Senate's floor proceedings, Senators feel under no obligation to come to the floor to record their presence. Quorum calls allow for such informal consultations, which may take place either on or off the Senate floor. Only if he or she finds that a quorum is not present does the presiding officer direct the clerk to call the roll. However, if the clerk finishes calling the roll and the presiding officer announces that a majority of Senators have failed to respond, the Senate cannot resume its business, including debate, nor can it dispense with the quorum call by unanimous consent, because the absence of a quorum has been established. In that event, the Senate usually has only two options: to adjourn or to take steps necessary to establish a quorum. The usual recourse is for the majority leader to make a motion directing the sergeant at arms to request the attendance of absent Senators. A voice or division vote is considered valid, no matter how many or how few Senators participated, unless a Senator takes the initiative to challenge the vote, before the result is announced, for violating the constitutional requirement that a quorum must be present for the Senate to do business:
Until a point of no quorum has been raised, the Senate operates on the assumption that a quorum is present, and even if only a few Senators are present, a measure may be passed or a nomination agreed to ... Voice votes may be taken on the passage of a bill and if no question of a quorum is raised, that action is final, even though a majority of the Senators did not participate; the Senate operates on the absolute assumption that a quorum is always present until a point of no quorum is made. Consequently, at least 11 Senators—one-fifth of the minimal quorum of 51 Senators—must raise their hands to support a request for a rollcall vote. It is not at all unusual, for example, for a Senator to offer an amendment and then immediately ask for the yeas and nays on that amendment even before the debate on it has commenced. Conducting Rollcall Votes

If a roll call has been ordered, when the time to vote arrives, the presiding officer states that "the yeas and nays have been ordered and the clerk will call the roll." If the yeas and nays are not ordered on the pending question, that usually indicates that there is no uncertainty among Senators about what the outcome will be.
The Constitution states that "a Majority of each [House] shall constitute a quorum to do business.... " The Senate presumes that it is complying with this requirement and that a quorum always is present unless and until the absence of a quorum is suggested or demonstrated. This presumption allows the Senate to conduct its business on the floor with fewer than 51 Senators present until a Senator "suggests the absence of a quorum."
Except when the Senate has invoked cloture, the presiding officer may not count to determine if a quorum is present. When the absence of a quorum is suggested, therefore, the presiding officer directs the clerk to call the roll. The Senate cannot resume its business until a majority of Senators respond to the quorum call or unless, by unanimous consent, "further proceedings under the quorum call are dispensed with" before the last Senator's name has been called. If a quorum fails to respond, the Senate may adjourn or take steps necessary to secure the attendance of enough Senators to constitute a quorum. It usually takes the latter course by agreeing to a motion that instructs the sergeant at arms to request the attendance of absent Senators.
More often than not, however, quorum calls are unrelated to attendance on the floor. Senators "suggest the absence of a quorum" to suspend the Senate's formal floor proceedings temporarily. There are many purposes for such quorum calls. For example, they can be used to permit informal discussions that are intended to resolve a policy disagreement or procedural problem, or to allow a Senator to reach the floor in order to make a speech or begin consideration of a bill. When a quorum call is provoked for such a purpose, it usually is ended by unanimous consent before the call of the roll has been completed.
The Constitution also provides that "the Yeas and Nays of the Members of either House on any question shall, at the Desire of one fifth of those present, be entered on the Journal." Any Senator who has been recognized may "ask for the yeas and nays" on whatever question the Senate is considering. If the yeas and nays are ordered at the request of at least 11 Senators (one-fifth of the minimum quorum of 51), that determines the manner in which the vote will be conducted (if it is conducted). The timing of the vote is not determined by this request. A Senator may offer an amendment and immediately ask for the yeas and nays, even if the vote is not expected to take place until hours or days later.
If the yeas and nays are not ordered, the Senate votes on questions by voice vote. Alternatively, if the presiding officer believes that the outcome is not in doubt, he or she may say that, "without objection, the amendment (or motion, etc.) is agreed to." If any Senator does object, a formal vote ensues.