In the two well referenced experiments [1, 2] that claimed to have observed double slit interference pattern of SINGLE electron, the central claim is that there could not have been more than ONE electron present at the same time in the apparatus (or such probability is negligible). However, can anyone explain their rational for that claim? I read the original paper , and a commentary on paper , but I cannot get a good understanding on how the experimenters made sure (or reasoned) that the electrons passed through the apparatus ONE by ONE (a concept to me even contradictory to the very implication claimed by them - the wave nature of electrons). If the presence of more than ONE electron at the same time is excluded with a high probability but not absolute certainty, how is this probability computed? 1. Merli, P. G., Missiroli, G. F., and Pozzi, G. : `Electron Interferometry with the Elmiskop 101 Electron Microscope', Journal of Physics E: Scientic Instruments, 7, pp. 729–732. 2. Tonomura, A., Endo, J., Matsuda, T., Kawasaki, T., and Ezawa, H. : `Demonstration of Single-Electron Buildup of an Interference Pattern', American Journal of Physics, 57, pp. 117–120.