I looked at the images of a few 9-point mirror cells on the Internet and noticed that the triangles are only attached with a bolt. Does this mean that they can also rotate, apart from the normal vertical movement? If this is the case, isn't there a chance that the rotation of the primary mirror can cause an unwanted rotation of one or more triangles, determining unequal mirror support?
Secondly, at page 186 Sidgwick says that "insufficient central support, allowing the axial region of the mirror to sag, will cause spherical over-correction" (pg 186, section 10, Amateur Astronomer's Handbook).
Can unwanted rotation of triangles cause spherical over-correction?
Thanks for your help