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Float Values (I’m new to Openplan)

3 replies [Last post]
will williams
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Joined: 13 Feb 2007
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I am having troubles with float values in projects. Let’s say I place a Finish No Later Than date on the critical deliverable. If the activity is negative the float runs through the project as I would expect. However when there is positive float on the critical deliverable the float value in the project is zero, even when finishing early.
The bottom line is if anyone can offer basic steps to determine the longest path (or critical path)with relative float values I would appreciate it greatly.

thanks again,


Gary Whitehead
User offline. Last seen 1 year 44 weeks ago. Offline
It’s been a while, but I think this is right:

The ’finish no later than’ constraint constrains the dates of the activity, not the float. In the absence of a project completion target date, Open Plan assumes it is equal to the Early finish of the final activity for calulating total float, hence you never get a positive project float.
(NB: I think the final activities ’free float’ will be the number you are looking for in this situation, but that’s a bit of a fudge)

You can assign a target finish date to the project from the ’project properties’ menu

Or you can use a ’target finish’ type of constraint instead of a ’finish no later than’ on your final activity. (NB: but not the ’fixed target’ type. This type basically says "this activity will finish on this date, regardless of logic or progress")


Paul Smith
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Joined: 14 Feb 2007
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Hi Will,
I’m guessing here but what I think you are seeing is the worst Case Float. If the Critical milestone is the last activity in the schedule then the float between this activity and the end of the schedule will be zero as the end date of the project is the same as the end date of this activity.
If you set a Project end date beyond the critical milestone then you will see a positive float value, ie contingency.
Samer Zawaydeh
User offline. Last seen 2 years 6 weeks ago. Offline
Joined: 3 Aug 2008
Posts: 1664
Dear Will,

The simplist and best way to understand the CPM is to use the Finish-to-start relationships.

A simple check of the internet will provide you with plenty of information; I found this one quickly.

From the basics you can gradually increase the difficulty of the relationship and the use of leads and lags and build up a program to suite your project.

Hope it will help.