How and When to determine Metrics From Application?

How do you determine metrics for your application?

Objectives of Metrics are not only to measure but also understand the progress to the Organizational Goal.
The Parameters for determining the Metrics for an application:
· Duration
· Complexity
· Technology Constraints
· Previous Experience in Same Technology
· Business Domain
· Clarity of the scope of the project

One interesting and useful approach to arrive at the suitable metrics is using the Goal-Question-Metric Technique.As evident from the name, the GQM model consists of three layers; a Goal, a Set of Questions, and lastly a Set of Corresponding Metrics. It is thus a hierarchical
structure starting with a goal (specifying purpose of measurement, object to be measured, issue to be measured, and viewpoint from which the measure is taken). The goal is refined into several questions that usually break down the issue into its major components. Each question is then refined into metrics, some of them objective, some of them subjective. The same metric can be used in order to answer different questions under the same goal. Several GQM models can also have questions and metrics in common, making sure that, when the measure is actually taken, the different viewpoints are taken into account correctly (i.e., the metric might have different values when taken from different viewpoints).

When do you determine Metrics?
When the requirements are understood in a high-level, at this stage, the team size, project size must be known to an extent, in which the project is at a "defined" stage.