One of the FARO® Laser Tracker's Kinematic Model Parameters of the tracker to compensate for Axis Non-Squareness or commonly just called Squareness. If this parameter has changed or is not optimized, it will result in a significantly higher Backsight or Two Faced error of a point on the floor at 135 degrees (or up in the air at a high angle) at a particular distance than a point at 90 degrees or on the horizon at the same distance.
CompIt has provisions to check this as well as correct it.
If the Pointing Compensation is not bringing the tracker into tolerance after the 6 points in a line are measured, then it will recommend to continue onto the Squareness Compensation, which consists of a few more points on the floor.
The Squareness parameter is a very stable parameter and does not change with temperature. Its changes are typically a result of shock, vibration or shipping. Some operators who ship the tracker to each inspection location may choose to go straight to the Advanced Tab of CompIT and run a full Pointing Compensation continuing onto the Squareness portion of the compensation despite the passing results up to that point to re-optimize the Squareness parameter for any small changes that may have occurred during transit.
For the ION / X / Xi trackers, if Self Compensation does not bring the tracker into tolerance after an Angular Accuracy Check, then it will recommend to continue onto the Pointing Compensation and Squareness Compensation. However, if the operator is measuring User Selected points and not following good measurement practices (i.e. – not checking backsights low or high despite measuring in those locations), then it is theoretically possible for CompIT to not determine that the backsights at high and low angles are not coming within tolerance and therefore not recommend to continue on to the Pointing Compensation. This is why it is always recommended to check backsight error around the measurement volume. This is also why a Pointing Compensation always follows Guided points with a point on the floor.
Keywords: Accuracy, Backsight, CompIT