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Estimation by definition is choosing a value using the best information available. The value needs to take into account the uncertainty involved. Keeping in line with the principle of Self Organization, the Guide to Scrum Body of Knowledge™
recommends the usage of Planning Poker to estimate tasks and other items. The usage of Planning Poker or Scrum Poker in the context of the Task Estimation Meeting is discussed below.

Planning poker is a collaborative estimation technique that leverages the collective wisdom of the team to produce more accurate estimates for user stories. By using a deck of cards with values representing effort or complexity, team members independently select their estimates for a given task, then reveal them simultaneously.

Planning Poker is a structured team communication mechanism to arrive at estimates by consensus. The Scrum Master acts as the moderator of the Task Estimation meeting. The Product Owner maybe present as an observer. All the participants are supplied with Fibonacci series or currency like cards that can be used to represent any number up to a certain value. A task or item that is well understood by all the participants is discussed, selected as the base task and a certain value is assigned to it. It is recommended that the value assigned be in terms of an abstract unit like story points or carrots.

In Planning Poker, each team member is assigned a deck of cards. Each card is numbered in sequence with each number representing the complexity of the User Story (or task) in terms of time or effort. The Scrum Team members assess the User Story (or task) to better understand it. Each member then picks a card from his/her deck that represents his/her estimate for the time or effort required to complete the User Story (or task). If the majority or all team members select the same card, then the estimate indicated by that card value will be the estimate recorded for that item. If there is no consensus, then the team members discuss reasons for selecting different cards or estimates. After this discussion, each member picks a card again. This sequence continues until all the assumptions are understood, misunderstandings are resolved, and a majority or consensus is reached. Planning Poker advocates greater interaction and enhanced communication among Scrum Team members. It also facilitates independent thinking by participants, thus avoiding the phenomenon of group think.

Planning Poker balances the problem of balancing group thinking vs individual thinking by having individuals take a stand before every participant’s stand is announced to all, thus avoiding the problem of anchoring. Also it uses relative estimation rather than absolute estimation due to the tendency of humans to be better at the former. Planning Poker is usually classified as a variant of the wide-band Delphi method

Planning poker is combination of analogy, expert opinion, and disaggregation in a fun way so that it will result quick and reliable estimates. All the team members are included in planning poker. On any agile project, you will have typically ten team members or less. If it does, the team can be split in twos. Then estimation is done independently by each team. The PO participates in planning poker but he or she doesn’t estimate.

At the beginning, each team member is handed deck of cards. All the cards are marked with a valid estimation number. Each member will be given a deck that reads a number series. The most popular of these estimation numbers are Fibonacci numbers. (1,2,3,5 ,8,13,2, 34,55 and so on). The cards are prepared before the planning poker meeting.

Then a moderator describes each of the user stories or theme that team is planning to estimate. Though generally the product owner acts as a Moderator, anyone can be a moderator. No special privilege or role is associated with the moderator. The product owner will answer all questions that the team members have.

The goal of estimation is to be somewhere on the left of the actual effort line. Important thing to remember is that this process is not about deriving an estimate that will resist all future inspection.

After all the queries are resolved, each team member selects a card that represents their estimation. Each estimator has to make a selection before Cards can be visible to everyone. Cards are kept private until everyone has estimated. Then the cards are turned over at the same time.
Then, all cards are instantaneously spun over and displayed so that all estimators can see each estimate. Chances are that these estimates will differ significantly. In that case, the high and low estimators will explain their estimates. The focus of this process is not to attack these estimators but to learn on what basis these estimations were assigned.

After this discussion, each team member will re-estimate by selecting a card. The earlier mentioned process will be followed again. Chances are that the estimates will meet by the subsequent round. Continue to repeat the process until all the estimators converge on a single estimate that can be used for the story. Very rarely it takes more than three rounds. Continue this process until estimates are moving closer together and they everyone converges on a single estimate.