Voting procedures in the Senate are a combination of formal procedures and informal practices, but there is method to the madness.

A roll call vote in the Senate is known officially as the “yeas and nays,” a term derived from

U.S. Senate Floor

Article 1 in the Constitution. Once a vote is ordered, the Senate’s Legislative Clerk calls the roll aloud, in alphabetical order. Few Senators tend to be around to answer to their name at precisely the right place in the alphabet.

The Clerk then calls the roll a second time, pausing to take Senators out of order as they either approach the desk or give a hand signal from the door of the cloakroom, from their desks, or elsewhere on the floor. The signal is usually a thumbs up or down. The Clerk repeats the signaling Senator's name and then "yea" or "nay" depending on the hand signal.

During this second roll call, you will notice that the Clerk may read several Senators names rather quickly and others more slowly. The ones read at a faster pace are the ones whose votes he has already noted. The others are read at a slower pace because he usually pauses to look up to see if they are present to give him a hand signal.

After the second roll call, the Clerk simply sits and waits for Senators to approach him, at the rostrum where he sits, or to give him a hand signal from the floor. He takes the votes as they come, in random order.

The Legislative Clerk's tally is the only official one, but majority and minority staff are simultaneously noting the votes at their respective party tables, right in front of the rostrum. When you are looking at the television screen, the Democratic table is on the left, and the Republican table is on the right. Senators will often enter the well during a vote and look at the vote tally sheets in progress being kept by their party’s staffers. They may also be studying the information sheets on the table which briefly summarize the matter being voted on, along with the party’s recommendation for that vote.

Another reason for all the milling around is that the roll call vote period is a chance for Senators to come together. It may be the only time during the day when they can see all of their colleagues in one place. Otherwise they are scattered around in their offices and committee rooms. It gives them a chance to chat with one another, about the vote in progress, or other business.

The roll call vote period is held open for at least 15 minutes, the minimum guaranteed in the rules. The rules set no maximum time, so votes can be routinely held open longer to accommodate Senators still getting to the floor. Senators often will have their staff call their party’s cloakroom and ask the vote be held open as they rush back to the Capitol from off the Hill somewhere, e.g. from a reception, meeting, or conference downtown.

There is a tension surrounding the length of the voting period. Majority Leaders constantly struggle to balance the requests of Senators who can’t seem to make it to the floor in the 15 minute period guaranteed them, with those who are irritated at the fact that votes routinely slip into 25-30 minutes in length thereby delaying other business to come and elongating the day’s proceedings.

After the guaranteed 15 minutes has expired, the decision of precisely when to close the vote and announce the final result is made and signaled to the Chair by the Majority Leader or his designee. After the vote is closed, the results are final. However, the Senate does permit Senators to change their vote afterwards IF the outcome will not change as a result and if unanimous consent is given for that purpose.

Senate rules actually say Senators are to vote from their desks but this is rarely enforced -- usually they do so only for matters of high importance or ceremony, e.g. an impeachment vote, treaty ratification, or Supreme Court nomination.