Abstract: The average evaporation rate over a predetermined area to be evaporated is controlled by moving an electron beam over said area wherein one characteristic of the electron beam is controlled in order to influence the evaporation rate. The electron beam is moved along a path according to stored maps wherein each position to which the electron beam is moved has assigned thereto substantially equal control values. In a first technique, each of the individual stored maps are selected in a sequential fashion to minimize the number of changes in the control value during a complete scan of the area being evaporated. In another technique, the control value of a predetermined position is compared against a predetermined number of stored control values, which is preferably all of the control values stored in a memory.