"Backfilling" means QuickAlign looks back in the measurement routine and creates partial alignments as required in order to accurately handle probe compensation of any non-3D feature.
Back-filling occurs if these conditions are met:
The measurement routine is in startup mode and therefore doesn't have a user-defined alignment.
One or more selected features for the QuickAlign operation is a 2D feature, such as a line, circle, or point.
A feature before the selected 2D feature exists that controls two degrees of rotation (LEVEL).
An Example
Measurement Routine before QuickAlign
Measurement Routine after QuickAlign
Back-filled alignment after PLN1
Back-filled alignment after LIN2
Final, fully constrained alignment