1. Chen, E.G. & Mu, C.J. (1990).New Development in Correction of Spherical Aberration ofElectro-Magnetic Round Lens.Int. Symp. Electron Microscopy, Beijing, China, Kuo, K. & Yao, J. (Eds.) pp.28–35.Singapore:World Scientific.
2. Crewe, A.V. (1992a).Electron motion in tuned fields, I. The algebra.Ultramicroscopy 41,269–277.
3. Hawkes, P.W. (1965).The geometrical aberrations of general electron optical systems.Phil Trans R Soc A 257,479–552.
4. Beck, V. & Crewe, A.V. (1974).A Quadrupole–Octupole Corrector for a 100 KeV STEM.Proc. 32nd Ann. EMSA Meeting, St. Louis, MO, Arceneaux, C.J. & Bailey, G.W. (Eds.), pp.426–427.Baton Rouge, LA:Claitor's Publishing Division.
5. Crewe, A.V. & Kopf, K. (1980b).A sextupole system for the correction of spherical aberration.Optik 55,1–10.