Scheduling is planning or arranging work-items or events to complete at a specific time. This would depend on how much Work is to be completed by how many Resources in what time Duration. Their relationship is governed by the simple formula :
Effort = Duration * Resource Units OR W = D * U
Before, we understand the equation, let us understand the variables involved:
Work or Effort:
This is the effort (independent of a resource) required to complete a task. Typically it is described in man hours. Effort indicated is irrespective of holidays and resources since not all resources may be working equal hours. For example, a contractor may be working half days (4 hours). So, if a task with work/effort=20h, will take 5 working days for completion. However, a resource with full day working (8 hours) will finish it in 2.5 working days.
Duration
This is the elapsed working time (excluding holidays and any other non-working exceptions). If today is Monday and you say "I want this report by Friday" you are indicating a duration. It does not mean that the resource must spend all their time to prepare the report. The actual report preparation may take only 5 hours. In this case 5 hours is the effort but the duration is 5 days assuming that there are no holidays in between.
Units
Allocation is a way to have a resource work on multiple activities at the same time. It can be specified as a percentage of daily working time or as a total number of hours that a resource must spend on the task.
For example, if a resource works 8 hour every day and you allocate that resource for 50% on a task, you are effectively saying - spend 4 hours on that task daily. If you enter allocation in hours it indicates that the resource should work a total of those hours on a task. In the above example, you want a 10 hour task to be completed within 5 days. To achieve this you can either enter the allocation as 10 hours or 25%. Assuming that the resource works 8 hours daily 2 hours per day is 2/8 * 100 % or 25%. Celoxis will allocate 2 hours daily to the task so that they will complete the task by Friday.
Let's take a few more examples so see how it works. For all these examples, assume that the 1 Man Day = 8 hours and all resources also work 8 hours per day.
A task takes 2 man days (16 hours) to finish and you assign a resource to work full time (i.e 8 hours per day). How long would it take? If you said 2 days, you are right. Let's see if the equation matches with our expectation. In this case, effort = 16 hours and resource allocation is 1 (i.e 100%). So duration = 16 ÷ 1 = 16 hours or 2 days since each day is 8 hours.
Assume that you add one more resource to the task. How long would it take to finish the task? Again, it's quite easy - 1 day. Both resources will work 8 hours each and finish the 16 hour task in a day. Let's see again if the equation matches with our expectation. In this case, effort remains 16 hours while allocation is 1 + 1 = 2. So duration = 16 ÷ 2 = 8 hours or 1 day. Again it does. If both of you are told to work only 2 hours per day i.e 25% (2 ÷ 8), then how long would it take? Effort remains 16 hours while allocation is now 0.25 + 0.25 = 0.5. So duration = 16 ÷ 0.5 = 32 hours i.e. 4 working days.
There are many other factors that impact task scheduling. Let us look at them.