Planning with PlanBee
How it works
PlanBee is a critical path planning tool. It allows you to specify tasks and their durations, and will then calculate the earliest and latest start and finish dates for each task, based on dependency links which you give it. It will calculate "Float", the amount of spare time that a given task has in the schedule as an indication of how important that task is to the overall timing of the project.
The results are made available to you in several forms, either for printing or for incorporation in other documents or programs.
"Float" for a task is defined as the number of days by which the finish of a task may be delayed without affecting the overall finish time of the project. Float can be calculated in terms of working days for that task or as calendar days, depending on an option on the Project Details panel (repeated on the Float and Criticality options panel). In the case of a task which uses calendar days for its duration specification, both options give the same result.
PlanBee reports the total amount of float in its main grid. However in the Gantt (bar) chart it further indicates the type of float.
Float which can be "used up" without affecting other tasks is known as "Free Float", float which will affect the timing of other tasks is known as "Interfering Float". PlanBee shades the edges of that portion of a bar which denotes interfering float. In task 132 above, free float exists from October 8th to 8:00 am October 16th and interfering float from October 16th to November 1st. This means that task 132's finish may slip to October 16th without causing a delay to any other task. If it slips beyond that date it will affect the timing of other tasks. All of the float in task 133 is interfering float, so any slippage will affect the timing of at least one other task.
Note that with PlanBee a "day" starts at 8:00 am and ends at 7:59 am on the following day. If a task has a duration of 1 day it will be considered to end on the day after it started and one minute before the start time. If the next day is a non-working day and the task duration is specified in working days, it will finish on the next working day.
If you are a new user of PlanBee, you may wish to experiment with the sample plans included. To access them, select the File Open menu selection or click on the button.
If a task has zero or negative float, that task is said to be "critical" and the sequence of critical tasks is called the "critical path" of the project. The float for critical tasks is displayed in red on the PlanBee spreadsheet view and you may highlight critical tasks in red in both the Gantt and PERT charts by clicking the appropriate check box in their windows (this also highlights the charts when printed on a colour printer).
In this example, any delay in task 326 will delay the finish of the entire project.
As an enhancement to the Gantt chart, PlanBee will optionally show dependency links:
The colours used are optional (you may change them by using an Options… menu item). Here links which are on the critical path are shown in red and others in magenta.
You may notice that sometimes a task on what looks like the critical path is not zero float. This can occur when some durations and lags are specified as "working days" and some are specified as calendar days. If a "working day" task is dependent for its start on a "calendar day" task, and the "calendar day" ends on a Saturday, normally the working day task cannot start until the following Monday. Therefore, the calendar task would have some float, because it could also continue on the Sunday if necessary.
If you "fix" one or more dates in PlanBee, all of the other activities are scheduled around them (this would usually happen when an actual finish date becomes known). Sometimes this cannot be done for some of the tasks and in those cases "negative float" arises. This is the number of days which must be "saved" if the fixed dates are to be met. Usually, you would assign additional resources to those tasks in order to reduce their durations.