The resources performance domain covers people, equipment, material and facilities. Team resources absorb most attention because they are the ones a project manager interacts with daily, and physical resources are where projects more often stall, because a delivery date that has already been missed cannot be recovered by anybody trying harder.
The properties that make them different are worth naming. Physical resources are ordered rather than assigned, they arrive on somebody else's schedule, they cost money to hold once they arrive, and many of them are consumed rather than released back for reuse.
Estimating what the work needs
Resource estimating asks what kinds and quantities each activity requires, and it is done alongside duration estimating rather than after it, because the two determine each other. An activity takes three weeks with one crane and eight with none.
The output is a set of requirements per activity and a resource breakdown structure that groups them by type and category. That grouping is what lets somebody see that fourteen activities all want the same specialist rig in April, which is not visible while the requirement sits inside each activity separately.
A resource calendar records when each resource is actually available, which is rarely the whole project. Equipment on hire for a defined period, a facility released by another project in June and a specialist available two days a week all constrain the schedule, and a plan built without them is a plan built against an availability nobody agreed to.
Lead time is a schedule input, not a procurement detail
The mistake that costs most is treating acquisition as something that happens after planning. An item with a sixteen week manufacturing lead has to be ordered sixteen weeks before it is needed, which means the design decision that specifies it has to be final well before that.
Working backwards from need date through delivery, inspection, installation and commissioning usually reveals that the real deadline is a design freeze months earlier than anybody had marked. That date belongs on the schedule as a milestone with the same weight as any other, because missing it moves the end of the project by the length of the lead time regardless of how the rest of the work goes.
Long lead items are also where hybrid arrangements originate. A component that must be specified and ordered early cannot be delivered adaptively, whatever the software around it is doing.
Levelling and smoothing are different acts
Both address a demand profile that peaks beyond what is available, and they differ in what they are allowed to move.
| Technique | Constraint respected | Effect on the critical path | Use when |
|---|---|---|---|
| Resource levelling | A hard limit on availability | May extend it, and often does | The resource genuinely cannot be exceeded, so the date gives way |
| Resource smoothing | The existing float only | Left untouched by definition | The date is fixed and the profile merely needs evening out |
Levelling is what you do when there is one rig and four activities want it. Something waits, the sequence changes, and the finish date moves. Smoothing is what you do when demand swings between three and eleven people week to week and the total is affordable, so activities with float are shifted to flatten the curve without touching anything on the critical path.
A resource histogram makes both legible. Demand per period as bars, availability as a line across them, and the bars poking above the line are the problem to be solved.
Holding cost is a real cost
Material that arrives early has to be stored, insured, protected from weather and theft, and often moved more than once. On construction and manufacturing work those costs are substantial, and they are the reason ordering everything as early as possible is not the safe answer it appears to be.
The opposing risk is that late delivery stops the work entirely. The judgement is between holding cost and delay risk, and it is made per item rather than as a policy. A cheap component with a reliable supplier can arrive close to the moment it is needed. A single sourced item with a long lead and no substitute justifies arriving early and being stored, because the cost of storage is small next to the cost of a stopped site.
Controlling them once they arrive
Physical resources need verification against what was ordered, condition inspection on receipt, and tracking of consumption against plan. Variance here is a leading indicator that reaches the cost report weeks later, because material consumed faster than planned means either waste, rework or an underestimate, and all three are cheaper to address on discovery.
Unused resources should be released rather than held, and release is the step most often forgotten at closure. Hired equipment still on hire, a facility still booked and a licence still renewing are costs the project continues to incur after it has finished, and they land on somebody who cannot explain them.
Where the exam puts the difficulty
Questions on this topic usually describe a situation where the obvious action is about people and the real constraint is physical. A team offering to work weekends does not shorten a curing time, and adding people to a site with one access route does not increase throughput.
The other reliable pattern is the levelling and smoothing distinction, framed as a scenario rather than a definition. If the question says the date cannot move, only float may be used, and the answer is smoothing. If it says the resource cannot be exceeded, the date is the variable, and the answer is levelling.