Next morning they inspected the site which had been almost cleared by the full team. Fred joined Gwilym and Bleddyn transferring the activities to a calendar. The first thing they did was mark off every Sunday and Holy Day from the calendar they had gotten from Father Drew. Then they wrote down, on each working day, which activities would be worked on that day. When they were done, they found that by following the plan they would be finished two weeks after Beltane.
Gwilym returned his gaze to the network diagram. “There are some activities here that could be sped up by taking men from other activities and putting them to work there.”
“But won’t that only slow down th’activities you take them from?”
“Aye, it will. But look at this.” He pointed out two strings of activities that both led to one common activity. “See how this first set of activities finishes on day 6 but the string below finishes on day 8. That means that this activity cannot start until day 9 because they both have to finish before we can do that one. So if I take men from the short string and add them to the longer one, maybe I can finish both strings in day 7. That will cut 1 day from the end of the project.”
“Where else can tha do that?”
“Let’s find all the places where strings come together and see.
The three identified all these activities of confluence and noted, in each case, which preceding string of activities finished last. Gwilym noted each one with a red dot. In one case he saw that the string he had noted led to an activity that was part of a string that later on was not colored red. That was because a different string leading to that same activity of confluence was longer still. He pointed this out to Fred and Bleddyn.
“There can be only one path that defines the length of the project. Look what happens if we go backwards. We start at the end, come to the first activity of confluence and follow the red dots to the second activity of confluence, then follow the red dots backwards all the way until we get to the start activity. All those other red dots don’t matter. We need to focus on this path. It is the critical path that defines the length of the project.”
“But Da, if you decrease the length of this ‘critical path’ won’t some of these other paths become critical?”
“Good point lad! We’ll have to keep an eye on them. But first, let’s look at the activities on the critical path and see which ones are most likely to be able to be sped up by adding more people.”
They noted some candidates.
When the crew came in for dinner, they asked them how the work was progressing. All the men seemed upbeat and Siorys estimated that they would be done by the end of today. After eating, some men gathered at the network diagram to find their activities. They asked what the red dots meant. Gwilym explained and the men nodded their agreement. “You stone masons always hold up my work,” groused one of the men.
“Our project must be finished by Beltane. The way we have it planned makes it finish two weeks late. We have to find ways to reduce the duration of some of these critical activities. Can we add men who are not being used at this time to these five critical activities to speed them up?”
The men gathered around and talked amongst themselves. “I’ll not be busy during that time,” volunteered one. “Perhaps so, but you’ll gum up the works,” joked another. The men talked it over with Gwilym and agreed that by adding men they could ‘crash’ parts of the project to bring the end date in closer to Beltane.
When the men returned to work, Fred helped Gwilym change the numbers on the network diagram and redo the calendar. This time they were only a day after Beltane.
“That’s all right, then Gwilym. They’re going to finish th’clearing a day early so we’ll be fine.”
“It’s too tight. Something always goes wrong in these projects and I’d like some room to move the project when that happens. We need a safety zone, a buffer. What else can we do?”
Fred studied the network diagram. “Here is a long string of activities that needs to be shortened. Do they all have to go after each other. Couldn’t we move one to the string above?”
“You mean do the activity in parallel instead of in series? Let’s see.”
The two men were joined by Bleddyn staring at the long string of activities.
“Building the stairs is slowing down a lot of activities. We can’t start it until the outside of the tower is built but we can’t do a lot of other activities until the stairs are in place. Can we build them independently of the tower and then move them in later?”
Fred laughed at this, then, seeing Gwilym’s expression, quieted and grew thoughtful. “We couldn’t build th’entire set of stairs outside th’tower but we could build all th’flights outside and then put them together inside. That would save a lot of time.”
Gwilym smiled and said, “Let’s ask the carpenter.”
The carpenter agreed and the new plan predicted them finishing a week before Beltane. Gwilym obtained a new hide and asked Fred to transfer the activities to this new sheet, making a clean copy of the plan they could use to build the tower.
“What do tha call these new tools, Gwilym?” asked Fred as he worked, humming his song.
Gwilym smiled. “What words are easy to rhyme with?”
“I can rhyme wi’ anything. Tell me what you call those tools.”
“Let’s see. First we estimated the duration of each activity, then we placed them in sequence, then we developed the schedule. We used a Network Diagram to visualize the schedule, then placed the activities on a calendar to manage them on a daily basis. Adding resources to an activity to speed it up is ‘Crashing’ and running two activities in series that are usually done in parallel is ‘Fast-tracking’”
Fred went back to work amusing Gwilym with occasional outbursts of “Network, Get work, Duration, Damnation, Nation, Sequence, Frequents.”
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