The resistance R of Fe, Pt and Cu films deposited by Ar ion beam sputtering was measured in situ and transmission electron micrographs of samples of different thicknesses were taken to identify the stages of film growth. A digital image processing technique was used to obtain the fractional coverage x as a function of film thickness t. Three stages of film growth are identified; the discontinuous and semicontinuous stages are modelled using a resistance network (10x10 grid) that represents the film for x<1 by equivalent resistors whose values depend on the grid intercepts with the film. The continuous regime is associated with t greater than or equal to t(min) where t(min) is the minimum that occurs in the R(t) measurements when plotted as Rt(2) vs. t. t(min) is shown to give a good indication of the onset of continuous film behaviour which first occurs at the point t(x=1), i.e when the film completely covers the substrate.