Merlin users will typically first become aware of this situation when working with activities scheduled to last more than one month. At first glance, something strange seems to be at work. The duration of the activity appears different compared to the time length entered by the user. Fortunately, the explanation for this is readily at hand when considering the concept of work units. The pure net hours are established in Merlin by entering values for “Work Units” under the Project Settings > General tab.

Let’s say that our activity should precisely begin at 8am on 1/1/2009 and last precisely one calendar year later at 8am on 1/1/2010. This corresponds to one year or 365 days. Merlin displays this differently, however, as actually 1.09 years. Why is it that Merlin doesn’t treat one year as exactly one year? Merlin calculates this expected duration with what is called pure net working hours. When you see how work units are calculated and notice the actual number of man work days per month is set to 20, things start to become a bit more clear. Given that a year is comprised of 12 months, each having 20 work days per month, this then when multiplied by 12 gives us a total of 240 work days per year. This of course differs from the 261 actual work days in a given year. This difference of 21 extra work days not calculated in Merlin is what results in the duration extending to 1.09 in duration for the year.

To remove the 1.09 Year duration from being displayed in the the Gantt chart, you can edit the view options for the activity bars. To do so, select “View Options” and select the “Styles” tab. Here you should select the middle label as shown and change the content setting from “Expected Duration” to another time unit, such as “Expected Work”.

Another consideration would be to change the setting for Calculated Durations under Work Units from “Dynamic” to “Days”. This way the activities will be displayed by working days. In our case, 261 days, for the calendar year.