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Figure 4. Network diagram of some piggery feeding operations.

most workers in the field, particularly ifit needed to be repeated frequently fordifferent planning criteria.

These same flow diagrams can beconverted into network diagrams whichconform to the conventions of CriticalPath Scheduling. Figure 4 shows howthis appears for some pig feedingoperations. The main advantage of thisrepresentation is that the activities canbe identifed by their node numbers andthat restraints and dummy activities ofzero duration can be introduced tosubstantiate the logic of the completenetwork, and provide for unique interpretation.

By applying the standard time datafor each activity, the time for eachroute through the network can becomputed. For this calculation, a number of variable factors such as totalfeed weight, number of feeds per dayand distance from feed stores to feeding area can be applied to give eacharrow a "length" in terms of units oftime or of $. These can be summed toshow the shortest or cheapest routethrough the maze for that set of circumstances represented by the valuesfor the variables.

A tabulation of the activities designated by their node numbers togetherwith the effect of the variables uponthem is given in Table 1. This is only apart of the total matrix described infigures 2 and 4.

used for either manual or computersolution for identifying the crtical paththrough a network, find the longestroute, as was mentioned in 1. abovefor the project as a whole. However forselecting the work routines, it is theshortest or cheapest route which is ofgreatest interest to managers. Thisminimal length of route as opposed tomaximum length of route can be accommodated by existing computer routines if the time date are assigned eithernegative values or reciprocal numbervalues in the calculations. This minormodification of routine is all that isrequired to adapt the basic computerprogramme. Sub-programmes are required for the addition of the calculations of the effect of the variable. Asonly trial runs for the computer haveso far been attempted, it is outside thescope of this paper to indicate how bestto include provision for the calculationsof variables.

CONCLUSION

While standard time data for themany alternative ways of performingwork in piggeries is already available,it will not be used by designers of newbuildings until it can be presented in amore convenient form. Yet it is thesevery designers whose influence on workmethods is almost irreversible once thebuildings are constructed. While thepossibility of using digital computers toperform the mathematical calculations

nodes until the last node is reached.This process is called the forward pass.Each node is then assigned a latestfinish date from a backward pass whichstarts at the terminal node of the network and is assigned to each node inthe reverse numerical sequence. Forthe longest pass solution each activitydependent upon its duration can be assigned to other dates. These are thelatest start possible without delayingthe whole project and the earliest finishpossible without delaying the wholeproject. Activities which have the sameearliest and latest start dates togetherwith the same earliest finish and latestfinish dates are said to lie on thecritical path.

For the shortest path solution, usedfor methods alternative analysis, theuse of reciprocal values of the durations will provide a solution which isthe shortest route.

Piggery Example

Figure 2 includes all piggery operations but for the sake of presentationthis paper will be confined to feedingalone. The principle can be expanded inscale quite simply, but becomes inconvenient for printing. The Flow ProcessCharts themselves could be used as an

aide memoire by a piggery planner tovisualize alternative methods for anyparticular units. However, althoughthis would be an improvement on thenormal clerical methods of using standard data, it would be a sufficientlyarduous methematical task to deter Normal C.P.S. procedures when continued on page 57

•ANADIAN AGRICULTURAL ENGINEERING, JAN. 1967 45