Hi,
I will show you something that makes MS PROJECT users crazy! Of course I’ll use MS PROJECT 2013.
I will first, create a Brand new Project with one Task with 5 days Duration, like this:
Everything is just fine. Now I will add one Resource with 24 Hours Calendar:
and I’ll assign this Robot to the Task:
or in Task Usage View:
So Robot will work 16 hours at Monday (From 8 AM till Midnight), and from 00:00 to 00:00 at Tuesday!
But, as you can see Task Duration is 5 days! WHY? the simplest answer is: Because MS PROJECT works that way.
The Magic Formula is: Duration = Work / Units. So, Work = 40 hours and Units = 100%. Since 1 Day is 8 hours, Duration = 40 / 100% (8 hours) = % Days.
It may look silly (actually it does), but MS PROJECT Calculates duration in that way, no matter which Calendar did you use. Duration of Project Summary Task is, on the other hand, Finish Date – Start date, and it is 2 days!
But, If you want to see “correct” duration for the Task, you can use, for Example, Duration 1 custom field with formula, like this:
and then:
and finally:
Now I will add this Field to the Gantt Chart, and I’ will get:
And I got what I wanted.
It’s a little bit Tricky, but well….
Regards!
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About Nenad Trajkovski
Location: Zagreb, Croatia
Occupation: Project Manager
Interests: Project Management and MS PROJECT
He was born in Zagreb, Croatia at 1963. After completing his college he started working on projects in different business areas (banking, manufacturing, automotive industry, distribution, oil companies, etc.) developing and implementing ERP systems into different companies. He has got a lot of experience working with people in different business processes and also possesses great knowledge in information technologies and financial services. Today he works as a business consultant, adn Project Manager in PERPETUUM MOBILE d.o.o. Zagreb. He is a regular lecturer for Project Management in MS Innovation Center in Varaždin, Logosoft Sarajevo in Bosnia and Herzegovina and SEAVUS GROUP in Skopje Macedonia. He was named the best lecturer of WINDAYS 2008 while his lecture was also voted as the best. In addition, he was in TOP 10 lecturers at the MS SINERGY 2009 and MS VISIA 2009, 2010. Shares first place as the best lecturer of KulenDays 2009 and 2010 and PMI Conference 2009 in Zagreb. He is also a regular lecturer in the MS Community. He is a Certified Accountant and a PMP (Project Manager Professional) and a PMI-RMP (Risk Manager Professional), MCP, MCT, and Microsoft Certified Technical Specialist - Microsoft Project 2010. From 01.01.2012 awarded with MVP (Microsoft Most Valuable Proffesional - Microsoft Project)!
Nenad Trajkovski 
Dear Nenad Trajkovski,
There might be something basic that you are overlooking. Duration is the amount of time available for working, not elapsed or default calendar or real time. And in the defaults (File > Options) you’ll find that 1 working day holds 8 working hours. Feel free to change that if needed. Now keep in mind that EVERY task and EVERY resource can be forced to have different calendars with varying hours pro day (Project > Change Working Time > Work Weeks). For the robot this means a 24 hours calendar as well as for the task it’s working on. Now the project summary task does not follow any specific calendar. It simply follows the default calendar and it starts at 8:00 at the creation of the project. If you want it to be 0:00 than YOU HAVE TO PUT IT ON THAT TIME MANUALLY using Project > Project Information. Now the task for the robot starts at 0:00 and finishes after 40 working hours (or 5 working days). The project summary task will show you the amount of working days BASED UPON THE DEFAULT CALENDAR. This results in 1,88 days for the project summary and 5 days for the robot task. Both are correct !!! Your work around using the ProjDateDif function shows actually the default calendar duration pro task. Without taking there own calendars into account. This column perhaps should be named like “defcal duration” or something?
Thanks for putting this problem on the web:)
Regards,
Theo