The absorption and MCD (magnetic circular dichroism) spectra of the origin band of the (1) Sigma(0)(+)-->(3) Pi(2) 5p-->6s Rydberg transition of HI are presented at the optimal resolution consonant with the generation of a reliable MCT) spectrum. The MCD spectrum is complicated and not readily interpretable. The absorption and MCD spectra have been simulated at three levels of resolution which involved calculation of the appropriate intensities (i) for each individual roelectronic transition, (ii) convolution of these in (i) with a shape function, and (iii) convolution of those in (ii) with an apparatus function. It is shown that excellent agreement of experiment and theory occurs, and it is suggested that the majority of MCD spectra of the rovibronic transitions of gas phase molecules may be amenable to such analysis.