Scheduling Fundamentals
Lag and Lead
Lag adds a waiting period between two linked activities; lead (negative lag) does the opposite, letting the successor start before its predecessor has actually finished.
Definition
Lag is a deliberate delay built into a relationship -- for example, waiting 3 days after concrete finishes pouring before starting formwork removal, to let it cure. Lead, expressed as negative lag, allows the successor to start before the predecessor is actually done, which isn't physically real the way a curing period is. DCMA's target for both is zero, not a percentage threshold -- any lead or lag at all is flagged as its own finding, because lead in particular is one of the most common ways a scheduler under pressure can hide missing float without touching the logic a casual reviewer would notice: the finish date holds, but only because an activity is allowed to 'start' before its predecessor is genuinely complete. A reviewer finding a handful of large leads buried in a schedule's logic can undercut confidence in the whole forecast, since it means the finish date isn't actually being driven by real, achievable sequencing.
Example
A relationship between 'Excavate Foundation' and 'Place Rebar' carries a -5 day lag (a lead) -- rebar placement is scheduled to start 5 working days before excavation is actually complete, which isn't achievable in the field and is quietly absorbing 5 days of float that doesn't really exist.