The Previous task field determines which task/s must be completed for a current task to be indicated as ready.
The resource should only start working on his task when it’s indicated as ready because only when the task is indicated as ready, meaning Previous task/s completed, all required assets will be available in the order for the resource.
Once indicated as ready, OOONA tool will be available to start working on the task (in integrated systems).
The selected Previous task value/s for a current task determines which task/s must be completed for the current task to be indicated as ready to be started working on.