 As a rule of thumb, for a 5 kV beam in air, it is required that the product p0L = 1 Pa·m or less.By this second principle of electron beam transfer, the design and operation of an ESEM is centered on refining and miniaturizing all the devices controlling the specimen movement and manipulation, and signal detection.The problem then reduces to achieving sufficient engineering precision for the instrument to operate close to its physical limit, corresponding to optimum performance and range of capabilities.