How lead/lag is handled when you export to another project management application

In Asta Powerproject, a link can have lead/lag at the start of the link, at the end of the link, or at both ends of the link. The lead/lag at the start of a link is calculated according to the predecessor task's calendar and the lead/lag at the end of a link is calculated according to the successor task's calendar. Where the predecessor and successor tasks use different calendars, the ability to position lead/lag at the start or the end of a link enables you to obtain precise and accurate positioning of tasks when you reschedule a project.

Other project management applications, such as Microsoft® Project and Primavera P6®, only allow lead/lag to be present at one end of a link. If a link in Asta Powerproject has lead/lag on both the start and the end of the link, the two values are combined into a single value during export.

The calendar that is used to resolve the lead/lag on a link differs from one application to another, as explained below.

Microsoft Project	Lead/lag is always calculated according to the successor task's calendar.
Primavera P6	Has a global option, the setting of which determines whether lead/lag is calculated according to the predecessor task's calendar, the successor task's calendar, or a 24 hour, elapsed time calendar.

In projects that are imported from Microsoft Project, lead/lag on links between tasks that use different calendars is calculated using the successor task's calendar. In addition to this, if a Microsoft Project file contains any links between tasks that use different calendars that have their lead/lag defined in terms of percentage rather than in terms of duration, this percentage lead/lag is converted to a fixed duration when the project is imported into Asta Powerproject.

As the calendar that is used to calculate the lead/lag is configurable in Primavera P6, you must find out how this setting is configured in the Primavera software before you export an Asta Powerproject project to be opened in either of these applications, so that you can specify the same setting during the export process - using the Calendar for link lag group on the Primavera XML & XER Export Options dialog:

If you calculate lead/lag using the predecessor task's calendar in Primavera P6, select the Predecessor radio button when exporting a project.
If you calculate lead/lag using the successor task's calendar in Primavera P6, select the Successor radio button when exporting a project.
If you calculate lead/lag using the 24 hour, elapsed time calendar in Primavera P6, select the 24 Hour radio button when exporting a project.

Selecting the wrong calendar option during the export process may result in the project rescheduling incorrectly once it has been exported.

This is illustrated by the simple project below:

Tasks positioned precisely using lead/lag

The project is exported. During the export process, the Predecessor radio button is selected in the Calendar for link lag group on the Primaver XML & XER Export Options dialog.

If, when the exported project is opened in Primavera P6, Predecessor Activity Calendar is selected in Advanced Schedule Options, the lead/lag is calculated according to the correct calendar (because the correct calendar option was selected during the export process), giving the correct results:

Predecessor Activity Calendar selected for scheduling relationship lag

However, if when the project is opened in Primavera P6, Successor Activity Calendar is selected in Advanced Schedule Options, the lead/lag is calculated according to the wrong calendar (because the wrong calendar option was selected during the export process), giving incorrect results:

Successor Activity Calendar selected for scheduling relationship lag

In this example, the lead/lag would also be calculated according to the wrong calendar if 24 Hour Calendar was selected in Advanced Schedule Options.