A set of more than 800 hourly ionograms recorded at Millstone Hill during July 89 and November 90 and inverted at the University of Massachusetts Lowell is the source of this study. This set contains the virtual and real-height profiles and the main classical ionospheric parameters. It is used in order to test the precision of different procedures leading to hmF2 the height of the maximum concentration in the F2 region, and also to establish the possibility of representing the real-height profile of the F2 region by a suitable generalized Chapman function.