C The F option used common features between the current image and a C reference image to compute the orientation of the current image C relative to the reference. This requires a shape model with similar C curvature to the actual shape. A sphere or triaxial ellipsoid is C usually sufficient but with favorable approach imaging and phases, C LIMBER can be used to refine the modl. If GraphicConverter is being C used, set up the side by side display and stretch it to show the C most common features. The scale should be set to display a bit of C curvature but not all the way to the limbs. In the GC Edit menu go C to "Record Mouse Clicks" and choose "Start". Then click on common C features alternating first left and then right until a number of matches C have been identified. Then go to "Record Mouse Clicks" and choose "Stop". C Again go to "Record Mouse Clicks" and choose "Copy" (to the clipboard). C Then open orcreade a file called gc.txt and paste the clipboard into it. C Unfortunately, the selected matches are measured from the left and bottom C rather than from the left and top. The program gc2reg produces a file C called reg.txt that corrects this. In REGISTER, open the F option and C paste the contents of reg.txt into the terminal window. Then type 0,0 to C end the entry. The .SUM file for the current image will be altered with C new CX, CY, CZ, V0 AND SZ reflecting the new orientation. Important note: C when exiting REGISTER withoption 0, enter 'n' so that the original .SUM C file will be restored.