In Australian commercial construction projects, a levelling instrument is a crucial tool used for determining and establishing accurate horizontal planes or levels across a construction site. These instruments are essential for ensuring that structures are built level and to the correct specifications.

Common types of levelling instruments used in construction include:

1. Automatic Level (Dumpy Level): This is a precise optical instrument used to establish or verify points in the same horizontal plane. It consists of a telescope mounted on a tripod, which can be adjusted to ensure it is perfectly level.

2. Laser Level: This is a more modern tool that projects a laser beam to establish a level line across a distance. It is highly accurate and can be used for both indoor and outdoor applications.

3. Digital Level: This instrument uses electronic sensors to provide digital readings of level differences. It is user-friendly and offers high precision.

4. Transit Level: Similar to an automatic level but with the capability to measure angles in addition to levels. It is used for both levelling and surveying tasks.

These instruments are vital for tasks such as setting foundations, aligning walls, installing ceilings, and other construction activities that require precise level measurements. Proper use of levelling instruments ensures structural integrity and adherence to design specifications in construction projects.