Voici les règles intégrales du Milestone (DMG p. 123):
Milestones
If the characters complete multiple encounters
without resting, they reach milestones. “Reaching a
milestone” means completing two encounters without
taking an extended rest. For every two encounters
the characters complete between extended rests, they
reach a milestone.
Awarding Action Points
When characters reach milestones, they get action
points. Action points help balance the depletion of
character resources (expended daily powers and healing
surges) by providing a new resource that can help
characters adventure longer before taking an extended
rest.
Characters have 1 action point when they complete
an extended rest. When they reach a milestone,
they gain another action point. They gain additional
action points after every milestone. When they take an
extended rest, they lose any unspent action points and
start the next day with 1 action point again.
Varying Action Point Rewards
You’re well within your rights to tell the players that
an encounter doesn’t count toward a milestone. An
encounter that’s two or more levels lower than the
characters is really easy, and it shouldn’t contribute
toward a milestone.
Likewise, if the characters overcome an encounter
that’s really hard, you can count it as two encounters,
so they reach a milestone right away. An encounter
that’s four or more levels higher than the characters
should count as two encounters.
If you vary encounter difficulty within a more
normal range—one level below to two or three levels
above the characters’ level—just count each encounter
as one. The harder encounters balance out the easier