PMGT1865 Chap.5 Schedule Formats, Gantt Charts and Planning Software
Schedule Formats, Gantt Charts and Planning Software
Once both passes are done you hold a complete schedule. What you do not hold is anything somebody outside the project will read. Schedules come in four formats, each a compression of the same underlying result tuned for a different audience, and knowing what each one throws away is the difference between choosing a format and defaulting to one. A schedule table is precise and shapeless.
A milestone chart is readable and shows no dependency at all. A network shows the logic and is hard to read. A bar chart sits in the useful middle and pays for its simplicity by discarding the dependency arrows, which is the expensive loss. This chapter also covers what planning software does and does not do.
It removes the redraw problem that makes manual charts cumbersome to maintain, and it hides the method, which is exactly why the unit teaches the calculation by hand first and then asks you to confirm that the tool agrees with you.
What this chapter covers
- 01
Four schedule formats, what each is best at, and what each discards
- 02
Placing the formats on two axes: how readable they are and how much logic they show
- 03
Matching the format to the decision the reader is about to make
- 04
Why the schedule table is the format everything else is generated from
- 05
Building a bar chart from the forward pass, one bar per activity at its early start
- 06
Drawing float as an extension to the late finish, and why that is what makes the chart usable
- 07
The three stated limitations: no visible interrelationships, no visible knock on effect, cumbersome manual change
- 08
What planning software derives from what you enter, and the four things it will not tell you
- 09
The manual against automatic scheduling switch, and the impossible critical path it can produce
- 10
Confirming the tool's critical path against the one you computed by hand
Converting a network and answering a delay request
- +1Place the bars at their early starts and mark A, C, D, F and G as critical, then draw the float tails: two days on B and three on E, and none anywhere else.
- +1Take the microphone request. E carries three days of float and the request is for four, so three days are absorbed and the fourth is not.
- +1Work the consequence. E now finishes at 18 against a late finish of 17, so F starts a day later and the project finishes on day 23. Tell the supplier that fourteen days costs the project one day and that the activity has just joined the critical path.
- +1Take the shell request. C is critical, so it has no float at all and three extra days is three extra days on the project, finishing on day 25. Tell the contractor there is no slack whatsoever and the request has to go to the sponsor as a change.
- +1State the general rule you have just used. A delay of d days on an activity with float f costs the project the greater of zero and d minus f, and critical activities have f equal to zero.
Key terms
- Milestone chart
- A schedule format showing only dated checkpoints. It is the easiest of the four to read and shows no dependency at all, which makes it a reporting instrument rather than a planning one.
- Bar chart
- A visual tool showing one horizontal bar per activity against a time axis. It combines planning and scheduling in a single picture and is popular because it is simple.
- Schedule table
- The row and column form carrying identifier, description, duration, predecessors, early and late dates and float. It holds strictly more information than any picture of it and is the only format checkable line by line.
- Float tail
- The dashed extension drawn from the end of a non critical bar to its late finish. Without it every bar on a chart looks equally urgent, and the chart cannot answer the question most readers actually have.
- Manual scheduling
- A software setting in which a task keeps the dates you typed and ignores its own predecessors. A plan mixing manual and automatic tasks can display a critical path that is arithmetically impossible.
Schedule Formats, Gantt Charts and Planning Software FAQ
Which format should I hand to which reader?
Match it to the decision they are about to make. A sponsor at a stage gate needs a milestone chart, because the question is whether to release the next tranche. A work package owner needs a bar chart filtered to their branch, because the question is what to do this fortnight. A planner assessing a change needs the network with float, because that question is about slack and slack lives in the logic.
A marker or an auditor needs the table, because that is the only form in which every number can be traced to the one before it.
Does a bar chart really not show dependencies?
The format itself does not carry them, and that is the limitation the unit names. Software will draw link arrows onto a chart, which helps, but a hand drawn chart in an assessment will not have them, and even with arrows the chart cannot show float or tell you which link is driving a date. The practical consequence is that a bar chart handed over without its network cannot be checked for feasibility by the person receiving it.
What is the point of learning the calculation if software does it?
Two points. The first is diagnostic: when a date moves in a tool you need to know why, and the only way to know is to understand what the tool did. The second is verification: the software week asks you to identify the critical path in the tool and confirm it matches the one you computed by hand, which means the tool is being checked against you rather than the other way round.
A planner who cannot do that has no way of noticing when a setting has quietly broken the logic.
Assessment move
Comparison questions are marked on the criteria you compare against rather than on the number of features you can list, so decide your criteria before you write. Four work well here: who the audience is, what the format makes visible, what it hides, and how it behaves when something changes.
Work through all four formats against all four criteria rather than describing each format in turn, and finish by choosing one for a stated situation and saying what you accept losing. An answer that never picks anything is worth noticeably less than one that does.
For the practical side, get into the habit of submitting a network and a bar chart together, obviously derived from each other: same identifiers, same durations, same critical activities marked. A chart whose critical path disagrees with its own network is among the fastest marks a marker can take, and it costs nothing to check. Sort the rows one way, say which way, and do not change it between drafts.
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