Fixing and flexing
Since PRINCE2 Agile is the same core method as PRINCE2, but tailored for an agile project context, PRINCE2 Agile uses the same 6 performance aspects as PRINCE2. These 6 aspects are time, cost, scope, quality, risk, and benefits.
PRINCE2 recommends the setting of tolerances for each of these aspects and by doing so, a project is defining who has authority to take decisions. For example, if the project board sets tolerances for the project manager, and these tolerances are forecast to be exceeded, this is known as an exception which requires escalating to the project board for a decision.
As variations from the agreed aspects start happening on a project, the project manager has authority to rectify these problems by using tolerances from another aspect, but only so long as none of the aspects are forecast to exceed tolerances. For example, suppose work becomes delayed. The project manager might be able to spend some of the cost tolerance within the plan to employ more resources to recover the lost time.
So, in PRINCE2, finding solutions to a performance aspect which is in danger of being breached by utilising another performance aspect is common.
Fixing time and cost
In an agile world, work is planned in iterations, commonly called sprints. These are timeboxes with a fixed time. In this regard, on agile projects there is zero tolerance for time. The work is always completed by the end of the sprint and work is planned based upon a prioritised set of requirements (often known as user stories on a backlog).
The way that an agile team deals with problems caused by something taking longer than expected is to change the scope of work within the timebox. This is done by doing work, which is essential first, then working on tasks which are not essential but are good to have, and finally working on tasks that are nice to have if there is still time left within the timebox.
Cost also has zero tolerance because in agile teams it is assumed that the team remains stable, at least for the duration of the timebox.
Therefore, the ability to rectify a problem in one performance aspect by taking from another performance aspect does not work in the same way on agile projects.
The hexagon in PRINCE2 Agile
PRINCE2 Agile represents the 6 performance aspects of PRINCE2 by a hexagon. Two of the corners on the hexagon (time and cost) are fixed i.e. they have zero tolerance. Two corners are flexible (quality and scope), and two corners may be fixed or they may be flexible (risk and benefits). The diagram below shows the six corners and whether they can be fixed and flexed.

Five targets
The rationale for fixing and flexing what is delivered is based upon understanding five targets. The 5 targets are:
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Be on time and hit deadlines.
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Protect the level of quality.
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Embrace change.
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Keep teams stable.
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Accept that the customer doesn’t need everything.
Hitting deadlines has significant benefits.
Delivering to the level of quality expected results in a lower total cost of ownership over the life of the products.
Change is inevitable and enables a more accurate final product.
Avoiding adding or removing people from a team during a timebox produces the most efficient team.
Accepting that not everything the customer thinks they want in the initial stage of a project is desirable.
Summary
The concept of fixing and flexing goes to the heart of PRINCE2 Agile. It enables project teams to deliver on time, without sacrificing quality by varying the scope of what is delivered by the project delivery team. This enables them to deliver what the customer really wants in an iterative and incremental way, allowing the customer to realise value early in a project.