In this Brief Report we study the measured and modeled Lyman- a intensity ratios for hydrogenlike Cl XVII in a deuterium base plasma in the Joint European Torus tokamak and examine the agreement between experiment and theory for a particular plasma shot. A collisional-radiative model is used to calculate the values of the intensity ratios using measured plasma parameters for comparison with line-of-sight values. When variations in the electron parameters during the discharge are taken into account, the variations in the modeled values are seen to follow the experimental data. The difference between the values of observed and modeled intensity ratios is discussed.