I am living proof that old dogs can learn new tricks. Did you know that the lowly Calcualtor built into Windows can do some basic date calculations? Neither did I until recently! Here's what I'm referring to.
Start the Calculator application. It looks like this:
Nothing unusual here--we've all seen and used the Calculator countless times. But have you ever seen the View menu? It looks like this:
Pick the Date Calculation command and you get this expanded Calculator:
When introducing Project's scheduling engine, I've sometimes asked my audience a smart-alec question along the lines of: "Quick,what's April 15 minus February 18?" My point being that it's difficult to do such calculations mentally.
Well, turns out the lowly Calculator application can answer such questions quite easily:
Who knew! Maybe you did, but I sure did not until recently.
Let's dig a little deeper into the answer, 56 days. The question the eager Project user is dying to ask is, "Is that 56 working days or 56 elapsed days?" The answer, of course, is elapsed days. In other words, these are all the days (weekdays and weekends, regular days and holidays) between the two dates I provided.
Now let's look at the same question in Project.
41 days and not 56 days? What gives?
The experienced Project user of course recognizes that Project's answer is in the form of working days. In this particular plan, that means Monday through Friday, but excludes weekends. If my project calendar had accounted for holidays between February 18 and April 15, the number of working days would have been reduced even further.
When estimating how long tasks will take, one critical clarifying question to ask is, "What restrictions do I need to account for regarding when work on this task can occur?" Such restrictions may include:
- Your organization's working and nonworking days (this may be, for example Monday through Friday are working days but Saturday and Sunday are not).
- Holidays and other events that will restrict work on what would otherwise be a working day.
- The availability of whoever will perform the work (in Project, you account for this via resource calendars; see these previous posts for more information).
- Restrictions in when work can occur due to the nature of the work (for example, work that must be performed only in the evenings, or only during the local dry season; in Project, you account for this via task calendars).
If this is starting to sound complicated, you're right! If you were relying just on the nifty Date Calculation feature of the Windows Calculator, you'd be in a lot of trouble because you'd very likely grossly overestimate the real span of working time between two given dates. Good news for Project users though: the calendar features of Project help you achieve much more accurate results when doing duration calculations.
Hands-on with Project Step by Step
To read more about this blog entry's subjects in the two most recent editions of Tim Johnson's and my Project Step by Step books, see the following cross-references.
The project calendar
Project 2010 Step by Step: "Setting Nonworking Days," pg. 46.
Project 2007 Step by Step: "Setting Nonworking Days," pg. 30.
Project 2010 Step by Step: "Adjusting Working Time for Individual Resources," pg.63.
Project 2007 Step by Step: "Adjusting Working Time for Individual Resources," pg.70.
Project 2010 Step by Step: "Adjusting Working Time for Individual Tasks," pg. 155.
Project 2007 Step by Step: "Adjusting Working Time for Individual Tasks," pg. 152.