Putting in the critical path

- The critical path is the longest path, and that's all it means. People often misunderstand this, and they think that the tasks on the critical path are the most difficult or expensive or the most failure-prone tasks. But they're not; they're just the ones that take the longest time to get done. So you can have trivial tasks, like routine paperwork on the critical path, and massive, expensive, important things that aren't on the critical path. So the first thing when drawing a Gantt chart is to put in the critical path. And it's always drawn coming down in steps like this. By the way, I'm using Excel to draw the Gantt charts on this course, but with Microsoft Project, it's similar. So why is it drawn coming down in steps? Well, the main reason is that you then have everything on its own line. So you can have extra columns off to the side for who's doing each task, which department they're in, that sort of thing. It also means that you can show slippage, what has actually happened compared with what should've happened. The main area we want to keep an eye on in terms of slippage is the critical path, because any of those tasks going late means that they'll push everything else late, and then the whole project will end up being delivered late. But floating tasks can also be a problem if they end up slipping, if they go so late that they affect the critical path. Now something that many people don't realize is that you can't really draw the Gantt chart unless you already know the critical path, because everything hangs off it. And the best way to get the critical path is to do a network diagram, which is one of these, quite often produced using Post-its, but you could use a computer to do it. So basically, you find the critical path by just adding up the times as you go across. Computers do it by doing something really complicated called a forward and backward pass. And some people teach that you should do this when you're doing it manually, but personally, I think that's just not necessary. Keep it simple, just look at the diagram. You can easily see what the longest path is. If you try to jump straight to the Gantt chart, you'll miss some dependencies and maybe get the wrong critical path. Even Microsoft Project does it in these two stages, really, but without you knowing. So when you enter tasks straight into the Gantt chart view, it is actually drawing the network diagram in the background. And in fact, you can click and view it if you want. But although this is clever, I actually think it encourages bad habits. If you let the computer draw the network diagram rather than doing it yourself, you run the risk of missing some dependencies, and therefore getting the wrong critical path. And then the foundation of your whole project plan will be wrong. If you start with a network diagram and then make it into a Gantt chart, it'll be quicker in the end than spending ages on your Gantt chart. You'll need about 20 minutes making the network diagram, probably using the Post-its, and then 10 minutes making it into a Gantt chart, and that's all you need, half an hour. And, it will be correct.