This paper reports on part of a development programme addressing fabrication of mirror segments for extremely large telescopes. Computer controlled corrective polishing using Zeeko's bonnet polishing technology and Precessions numerical optimisation, requires accurate tool influence function data. Stability and determinism of the influence functions are crucial for successful form-correction. Particular challenges arise when polishing up to edges, and correcting edge-profiles, because the geometry of the influence function created by an inflated bonnet changes as it encroaches the edge.
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