A constraint is a way to restrict the range that an object may move in time. If an attempt is made to graphically move an object past its constraint date, it will be blocked. Only activities and milestones may be constrained. NetPoint supports two types of constraints: a no-later-than (NLT) constraint, which defines the latest date an object may slide in time; and a no-earlier-than (NET) constraint, which defines the earliest date an object may backslide in time.
Constraining Activities
Both NLT and NET constraints may be set on the finish and/or start nodes, respectively, of an activity. An NLT constraint will restrict an activity from finishing later than the chosen date. An NET constraint will restrict an activity from starting earlier than the chosen date. Floats and drifts of constrained activities calculate from constraint dates.
Setting a Constraint
To set a constraint, double-click the activity to open the Activity Object window and click the Dates tab.
Check the Start Constraint or Finish Constraint box. The date will default to the current start or finish date.
To change the constraint date, enter the date or click the down arrow 
button next to the date field to open a graphic calendar picker.
Selecting a date on the calendar closes the graphic calendar picker.
When finished, click OK to exit the window and apply the constraint.
Visual Notification of a Constraint
A constraint is represented by an exclamation mark at the start node, finish node, or both:
Constraining Milestones
An NLT constraint can only be set for a start milestone. An NET constraint can only be set for a finish milestone. An NLT constraint will restrict a milestone from starting later than the chosen date. An NET constraint will restrict a milestone from finishing earlier than the chosen date.
Setting a Constraint
To set a constraint, double-click the milestone to open the Milestone Object window. Only the available constraint will be shown for application to the milestone. A start milestone is shown for this example.
Check the No Later Than checkbox. The Date field will default to the current date. To change the constraint date, enter the date or click the down arrow button next to the date field to open a visual calendar picker. Selecting a date on the calendar closes the calendar picker.
When finished, click OK to exit the window and apply the constraint.
Visual Notification of a Constraint
A constraint is represented by an exclamation mark placed in front of or after the milestone:
Start milestone constrained (NLT).
Finish milestone constrained (NET).
Tip: To avoid tracking behavior, use a benchmark. Benchmarks are constrained to the date that they’re set at and allow negative-gap to measure movement beyond the set date.