Task types duration units and work

Task types: duration, units and work

You put one plasterer on the plastering and the task takes four days. If you add a second plasterer, the work can be done in two days. It can also stay four days, with twice as much work in it. Both make sense. Which of the two the app picks depends on the task's task type. In this article you read how the app ties duration, units and work together and what each task type holds constant.

The concept

Three quantities are tied together:

• Duration: how long the task runs, in work days or in hours.
• Units: how much of a resource works on the task per work day. In the Properties panel this is called Units, in other windows Units/day. Units of 1 is one plasterer for the whole day, 2 is two of them and 0.5 is half a day.
• Work: the total number of hours the resource spends on the task.

The sum is: work = duration × units × hours per work day. The hours per work day come from the task's calendar. Plastering of four work days with one plasterer is, with an 8-hour work day, 4 × 1 × 8 = 32 hours of work.

If you change one of the three, at least one of the other two has to move along, otherwise the sum no longer holds. The task type decides which one. You set it per task, in the Properties panel. The app only shows the task type and the work once you turn them on; how that works is in Choosing a task type.

A task type only works on ordinary tasks. Milestones, phases (summary tasks), hammocks and tasks whose Duration type is Elapsed time do not have one: the Task type field is not there. Material, such as concrete or plaster mortar, does not count either. The quantity of material never drives the duration and the app never adjusts it because of a task type.

How the app calculates

The task type acts on what you change

The app recalculates duration, units and work only at the moment you change one of them: the task's duration, the units of an assignment, the work, a resource added or removed, or the hours per day in a calendar. Calculate (F5) changes none of them: F5 only calculates dates. Choosing a task type does not change a single number either. The task type counts at your next change.

If a task type changes the task's duration, the schedule becomes out of date. The status bar then says Out of date — recalculate (F5), unless Calculate automatically is on.

Four task types

In the Properties panel there is an i icon next to the Task type drop-down. Point at it, click or tap it, and the app explains the task type that applies now. In the open drop-down each option has such an i icon too. The explanation starts with a bold sentence. The four task types, with that sentence from the app:

• Fixed duration and units (Work follows from duration and units.). This is the default. The app never changes the duration itself and the work follows from duration and units. If you type the work yourself, the app adjusts the units, because the duration is fixed.
• Fixed duration and work (Units follow from duration and work.). The app never changes the duration itself. If you change the duration, the work stays and the units adjust.
• Fixed work (Duration follows from work and units.). The work is fixed and the duration follows from work and units.
• Fixed units (Duration follows from work and units.). The units are fixed and the duration follows from the work.

So two task types leave the duration alone. With the other two the duration moves along when you change the units, the work or the number of resources. With one resource, Fixed work and Fixed units do exactly the same there. They differ when you change the duration yourself: with Fixed work the work stays and the units adjust, with Fixed units the units stay and the work grows along. They also differ when there are more resources on the task (see below).

The worked examples below show what each task type does.

Rounding

The duration that follows from the sum is rounded up by the app. For a task in days that is to whole work days, for a task in hours to whole minutes. Work and units stay what you entered or what the app took from the sum. As a result the sum sometimes no longer holds exactly. The example below shows what happens then.

Several resources

If a task has several resources, two agreements apply. With Fixed duration and work, Fixed work and Fixed units, the total work stays the same when you add or remove a resource. The app then divides it in proportion to the units. With Fixed duration and units, a new resource brings its own work instead. With Fixed work and Fixed units the slowest resource decides the duration: per resource that is the work divided by the units, and the largest result counts.

An example: two resources each have 32 hours of work and units of 1, 4 work days together. You set the units of the first to 0.5. The duration then becomes 8 work days. Under Fixed work the second resource keeps its 32 hours of work and its units drop to 0.5. Under Fixed units the second keeps its units of 1 and its work grows to 64 hours.

Progress

If the task already has progress, the task type works on the remaining part: the remaining duration and the remaining work. In the Properties panel that work is in the column Work (h). What has been done stays.

Tasks in hours

A task you plan in hours calculates the same, but in minutes. If only the crane is on a 5-hour task, that is 5 hours of work. Under Fixed work, the duration for units of 2 then becomes 2.5 hours. The hollow-core floor in the practice project also has the carpentry crew on it. It still needs 5 hours of work, is the slowest, and so the duration stays 5 hours. How hours and days relate is explained in Days and hours.

Worked example: the plastering

The example is the tutorials' practice project House extension. In tutorial 5 you work this out yourself and check the numbers. Here you read what each task type does.

The plastering takes 4 work days. One plasterer is assigned to it, with units of 1, and the work day is 8 hours. So the work is 32 hours.

Fixed duration and units

• You make the duration 6 work days: the work grows to 48 hours, the units stay 1.
• You set the units to 2: the duration stays 4 work days, the work becomes 64 hours.
• You type 48 hours in Work (h): the duration stays 4 work days, the units become 1.5.
• You assign a second resource, for example Plasterer 2, with units of 1: the duration stays 4 work days and that second one brings 32 hours of work, 64 hours together.

Fixed duration and work

• You make the duration 6 work days: the work stays 32 hours, the units drop to 0.67.
• You set the units to 2: the duration stays 4 work days. Because the duration is fixed, the work grows along to 64 hours.
• You type 16 hours in Work (h): the duration stays 4 work days, the units become 0.5.
• You assign a second resource, for example Plasterer 2, with units of 1: the 32 hours are divided, 16 hours each, and the units become 0.5 for both. The duration stays 4 work days.

Fixed work

• You make the duration 6 work days: the work stays 32 hours, the units drop to 0.67.
• You set the units to 2: the work stays 32 hours and the duration becomes 2 work days. This is the step you take in tutorial 5.
• You type 48 hours in Work (h): the units stay 1 and the duration becomes 6 work days.
• You assign a second resource, for example Plasterer 2, with units of 1: the 32 hours are divided, 16 hours each, and the duration becomes 2 work days. Remove that second resource again and the duration is 4 work days again.

Fixed units

• You make the duration 6 work days: the units stay 1, the work grows to 48 hours.
• You set the units to 2: the work stays 32 hours and the duration becomes 2 work days.
• You type 48 hours in Work (h): the units stay 1 and the duration becomes 6 work days.
• You assign a second resource, for example Plasterer 2, with units of 1: the 32 hours are divided, 16 hours each, and the duration becomes 2 work days.

When the sum does not come out

Under Fixed work you set the units to 3. The work is 32 hours, so the duration becomes 32 ÷ (3 × 8) = 1.33 work days. The app rounds that up to 2 work days. Work (32 hours) and units (3) stay, but 2 × 3 × 8 is 48 hours. The histogram therefore spreads the 32 hours over the 2 work days: 2 units per day, not 3. In the Work (h) field a warning sign appears, Differs from units × duration, to show this.

With two resources with different units it works the same way. If, under Fixed work, you add a second resource, for example Plasterer 2, with units of 2 to the plasterer with units of 1, the app divides the 32 hours in the ratio 1 : 2, so 10.7 and 21.3 hours. Both then need 1.33 work days. The duration becomes 2 work days.

A file from P6 or MS Project can also hold a Work (rem.) that is not equal to units × remaining duration. The same warning sign then appears. The app does not change this work by itself. If you change the duration of such a task, the app follows the task type, also when the remaining work came from the file. Under Fixed duration and units and Fixed units the remaining work becomes units × new remaining duration. Under Fixed duration and work and Fixed work the work stays and the units adjust. If a remaining work from the file disappears this way, you get a notification with the old and the new number of hours. Ctrl+Z restores the old value. The explanation at the warning sign tells you per task which of the two happens.

A different calendar

Under Fixed work the calendar's work day goes from 8 to 6 hours. The work stays 32 hours, so the duration becomes 32 ÷ 6 = 5.33, rounded up to 6 work days. How the app counts work days and work hours is explained in Calendars and working days. The app reports: After the calendar change the task type adjusted the duration of 1 task (work stays, hours per day changed).

A task with progress

The inner cavity leaf takes 5 work days and is 40% done: 2 work days are done and 3 work days (24 hours) remain. Under Fixed work you set the units from 1 to 2. The remaining work stays 24 hours and the remaining duration becomes 1.5, rounded up to 2 work days. The task now takes 2 + 2 = 4 work days and the progress is 50%. The percentage moves along, because the part that is done stays the same and the remainder gets shorter.

Consequences and misconceptions

"Fixed work means the duration is fixed." No, quite the opposite. With Fixed duration and units and Fixed duration and work the duration is fixed. With Fixed work and Fixed units the duration follows from the other two.

"If I choose a task type, my schedule changes." No. Choosing changes no number. Only at your next change does the task type decide what moves along. Under a task type that protects work, the app fixes the work at the moment you choose, so there is a number to protect. Such a task then has a stored Work (h).

"The duration changed without me touching it." That can happen after a change to the units, the work, the number of resources or the hours per day, under Fixed work or Fixed units. The status bar then says the schedule is out of date. Press Calculate (F5) to see the new dates.

Without an assignment a task type does nothing. There are then no units and no work to tie to the duration.

Files from MS Project or Primavera P6 always show the task type. For a task from MS Project the app sometimes keeps the effort-driven setting. That stored setting changes two cases. With Fixed duration and work and effort-driven, the work moves along when you change the duration, instead of the units. With Fixed units and not effort-driven, the work moves along when you add or remove a resource, and the duration stays. Tasks you create in the app do not have this setting. The explanation behind the i icon takes this setting into account.

See also

• Choosing a task type: the steps to set a task's task type.
• Assigning resources with a curve: putting a resource on a task, with units and distribution.
• Days and hours: how the app converts days and hours.
• Calendars and working days: how the app counts work days and work hours.