Feeds

A race to the finish

Pert, critical path or crawl to the line?

  • alert
  • submit to reddit

The Power of One Brief: Top reasons to choose HP BladeSystem

Project management Would you run 145 miles from Birmingham to London non-stop for fun? Of course not, but most years about 80 “ultra” runners do just that. They share the loneliness of the long distance project manager.

These brave souls running the Grand Union Canal Race risk exhaustion and collapse on some lonely stretch of canal but most of them complete the course in times of between 33 and 40 hours. Britain’s longest, and some say toughest, running race is a good analogy for most projects. Entrants discuss at length their game plans – what to eat and drink, how many stops to take, what support to call on, how to cope with stress, and so on. And of course they meet unforeseen circumstances, from getting lost to nipple rash.

The average project manager (PM) can probably relate to the problems of the typical Grand Union Canal Race competitor (if not the rashes). And like these runners, PMs try as hard as possible to build robust plans to reach the objective.

For the past 50 years or so, the question has been what is the best way to model any complex activity – and whether you need specific software to do it.

Though less favoured than in its heyday, Pert (program evaluation and review technique) and the critical path method (CPM) remain cornerstones in project modelling. Pert was invented by a couple of US Navy bigwigs in 1957 to manage nuclear submarine maintenance. Subsequently it was used on huge projects such as the Grenoble Winter Olympics. CPM, developed slightly earlier, is seen as the forerunner to Pert and is sometimes amalgamated within it.

Pert is best known for its network charts, derived from the raw data about all the activities to be undertaken. The chart acts as a metaphor for the flow of time (left to right) and provide an easy visual indication of the dependencies between activities.

Project plan: the stuff in red is the critical path.

Like our canal runners, the PM’s number one obsession when embarking on a project is estimating total duration. How fast can we go?

Pert’s primary deliverable, calculated automatically from the raw data, is the so-called critical path, or the minimum time needed to complete the project, and the listing of linked activities in that minimum path. Once the critical path is calculated, earliest and latest start and finish times for non-critical activities also fall out, and the implications for resourcing and scheduling.

Typically, you number activities or events sequentially (10, 20, 30...), allowing for later additions if needed. An event on the Pert chart is a block, linked to other events in the correct sequence, setting out the order in which events unfold.

The raw data consists of the activity name, and optimistic, pessimistic and expected durations. Different calculation methods may be used to estimate a duration time. Microsoft Project, for example, uses a weighted average from which the critical path is derived.

Once this is done “slack” (or “float”) becomes evident in those activities not on the critical path. Slack is the length of time an activity can be delayed without affecting the critical path.

The Gantt chart displays the critical path, colour-coded. The simplicity of the Gantt chart, and the clarity with which it shows the flow of time, makes it the preferred and primary chart on many projects. Change the data, and the critical path and the Gantt charge change too.

The Essential Guide to IT Transformation

More from The Register

next story
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
NO MORE ALL CAPS and other pleasures of Visual Studio 14
Unpicking a packed preview that breaks down ASP.NET
Secure microkernel that uses maths to be 'bug free' goes open source
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
Cheer up, Nokia fans. It can start making mobes again in 18 months
The real winner of the Nokia sale is *drumroll* ... Nokia
Put down that Oracle database patch: It could cost $23,000 per CPU
On-by-default INMEMORY tech a boon for developers ... as long as they can afford it
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
Google shows off new Chrome OS look
Athena springs full-grown from Chromium project's head
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Securing Web Applications Made Simple and Scalable
Learn how automated security testing can provide a simple and scalable way to protect your web applications.