It’s easy to get confused or overly concerned about measuring velocity. Actually, the concept is almost embarrassingly simple. Velocity in Agile is simply the number of units of work completed in a certain interval. Like in many fields, Agile proponents appropriated existing terminology.

Here is one typical definition, from agilesoftwaredevelopment.com:

In Scrum, Velocity is how much product backlog effort a team can handle in one Sprint. Velocity is usually measured in story points or ideal days per Sprint… This way, if the team delivered software for 30 story points in the last Sprint their Velocity is 30.

Velocity as a capacity planning tool used in Agile software development is calculated from the results of several completed sprints. This velocity is then used in planning future sprints.

The concept of velocity comes from physics. In physics, velocity is speed and direction, in other words, the rate of change of position of an object. Speed can be measured in many different ways.

In software, speed is frequently measured as size per unit of time (sometimes this has been called delivery rate). The measure of size could be any of the common size measures: lines of code, function points, requirements, changes, use cases, story points. The measure of time could be calendar time (month, week, day) or it could be specific to a project (sprint, release). As to direction, in software hopefully the direction is positive, but sometimes projects go backwards (for example, backing functionality out of a system).

Scope creep is a frequent topic of discussion among project management professionals.  A recent Project Management Institute (PMI)^® i Community Post, Fighting the Dreaded Scope Creep, reported some responses PMI members offered as their weapon of choice.  The various suggestions can be summarized by two general practices:

• Avoid making on-the-spot decisions (uninformed or politically motivated)
• Communicate the impact of the change to stakeholders and let them decide (analyze the cost, schedule, and risk impact)

Regardless of the specific practice, all of the recommended defenses included some process for change control.

I like words.  When I need to understand a topic, I pull the dictionary off the shelf (or access the online version), and look at the basic definition.  To determine why scope creep is such a formidable enemy, I looked up the word “creep”:  2. to approach slowly, imperceptibly, or stealthily; 4. to sneak up behind someone or without someone's knowledge.  A vast majority of results from a general internet search defined scope creep as “uncontrolled change.” 

Sizing is arguably the most challenging part of any software estimate. Without a notion of functional size, managers may find it difficult to negotiate realistic schedules based on their demonstrated ability to deliver software. They are unable to show empirically why the twelve person team that worked so well on a 150,000 ESLOC project over six months not only fails to deliver a 75,000 ESLOC project in half the time, but produces an error-ridden product that infuriates the customer. Unlike manufacturing shoes, software development is full of non-linear relationships between size, time, effort, and defects. What data driven estimation does successfully is arm managers with the ability to sanity check their current plans against past performance and negotiate achievable outcomes based on a realistic assessment of how much functionality can be built with a set time frame and resource profile.

So how do project managers get a better handle on size? The best place to start is with establishing a practical method for size estimation.

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