1. A method for observing a feature using a dual charged particle beam system, comprising: (a) directing an ion beam toward a substrate to mill a trench in the substrate, the trench exposing a vertical wall having an area around the feature to be observed; (b) directing an electron beam toward the vertical wall to form an electron beam image of the feature; (c) locating the feature; (d) measuring the dimensions of the feature; (e) analyzing the dimensions obtained from step (d) and determining an area size and location to mill and image a subsequent milling and imaging step by using a subsequent cross section that is exposed with the ion beam; (f) repeating steps (a) through (e).