Project scheduling has come a long way since the pyramids. Find out how Gantt developed his chart and how scheduling evolved along with computers.
The science of scheduling as defined by Critical Path Analysis (CPA) celebrated its 50th anniversary in 2007. In 1956/57, Morgan Walker and James Kelley Jr started developing the algorithms that became the Activity-on-Arrow or Arrow Diagramming Method (ADM) scheduling methodology for DuPont. The program they developed was trialled on plant shutdowns in 1957 and their first paper on critical path scheduling was published in March 1959.
The Program Evaluation and Review Technique (PERT) system was developed at around the same time but lagged critical path method (CPM) by six to 12 months, although the PERT team first coined the term ‘critical path’.
Later, the Precedence Diagramming Method (PDM) was developed by Dr John Fondahl in 1961 as a non-computer alternative to CPM, and the Metra Potential Method (MPM) was developed independently in Europe. Arguably, the evolution of modern project management is a direct consequence of the need to make effective use of the data generated by the schedulers in an attempt to manage and control the critical path.
Scheduling and computers
The evolution of CPM scheduling closely tracked the development of computers. The initial systems were complex mainframe behemoths, typically taking a new scheduler many months to learn to use. These systems migrated to the mini-computers of the 1970s and 1980s but remained expensive, encouraging the widespread use of manual scheduling techniques, with only the larger or more sophisticated organisations being able to afford a central scheduling office and the supporting computer systems.
The advent of the micro-computer (i.e. personal computer) in the late 1980s changed scheduling forever. The evolution of PC-based scheduling moved project controls from an environment where a skilled cadre of schedulers operating expensive systems made sure the scheduling was ‘right’—and the organisation ‘owned’ the data—to a situation where anyone could learn to drive a scheduling software package, schedules became islands of data sitting on people’s desktops and the overall quality of scheduling plummeted.
Current trends, back to enterprise systems supported by PMOs, seem to be redressing the balance and offering the best of both worlds. From the technology perspective, information is managed centrally, but is easily available on anyone’s desktop via web-enabled and networked systems. From the skills perspective, PMOs are redeveloping career paths for schedulers and supporting the development of scheduling standards within organisations.
The concept of scheduling is not new; the pyramids are more than 3,000 years old, the granite beams needed to support the roof of the burial chamber in the Great Pyramid required a workforce of several hundred, working for 10 years to hack them from their quarry by pounding the granite with a harder rock, dolomite. Teams were sent to the quarries in sufficient time to ensure the beams were available when needed on the construction site. Similar organisation can be seen on many other major projects since!
These activities could have been accomplished without some form of schedule; that is, with the understanding of activities and sequencing. However, while the managers, priests and military leaders (at least the successful ones) controlling the organisations responsible for accomplishing the works must have an appreciation of scheduling, there is little evidence of formal processes.
Modern schedule control tools can trace their origins to 1765. The originator of the ‘bar chart’ appears to be Joseph Priestley (1733-1804); his ‘Chart of Biography’ plotted some 2,000 famous lifetimes on a time scaled chart: “…a longer or a shorter space of time may be most commodiously and advantageously represented by a longer or a shorter line.”
Priestley’s ideas were picked up by William Playfair (1759-1823) in his Commercial and Political Atlas of 1786. Playfair is credited with developing a range of statistical charts including the line, bar (histogram), and pie charts. The atlas contained 43 time-series plots and one histogram.
Following on from Playfair another European, Karol Adamiecki, a Polish management researcher, developed the Harmonogram, also known as the Harmonygraph in 1896. The time-phasing and duration of the activities is shown by a vertical sliding tab, essentially the same as a bar in a bar chart. Of greater significance, the Harmonygraph also tabulates each activities predecessors and successors (‘from’ and ‘to’) making it a distinct predecessor to the CPM and PERT systems developed some 60 years later.
Henry Gantt, popularised the bar chart (Gantt Chart) in the USA through his books published in the early 20th century.
Other techniques dating from the early part of the 20th century include Line of Balance (flow line) used on the Empire State Building in the 1930s and Milestone charts, which were in regular use by the 1950s.
The key problem with Milestones and bar charts is all of the dates and durations are based on heuristics (rules of thumb) and/or experience. It was possible to identify slippage, but any assessment of the impact of a delay was based on a personal view of the data rather than analysis. As a consequence, when schedule slippage became apparent on major contracts, the tendency was to flood the work with labour and ‘buy’ time, frequently at a high premium.
The key value contributed by CPM and PERT systems was the ability to model future outcomes based on progress to date and optimise the use of scarce resources.
The evolution of scheduling has been a fascinating journey:
- Kelley and Walker set out to solve the time-cost conundrum and invented CPM: for most organisations the resolution of time-cost issues is still in the ‘too hard’ basket!
- The PERT project invented the name ‘Critical Path’, and everyone else borrowed it.
- Dr John Fondahl invented a non-computer methodology for scheduling that is now used by every computer package worldwide.
- And while Kelley and Walker’s CPM system was developed for computers, it is now primarily seen as a manual technique.
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