As a first step in determining a full absolute sensitivity calibration for the present KT7 spectrometers a relative calibration for the KT7/2 spectrometer is presented. This has been achieved using a novel approach, which proved particularly successful in the short wavelength calibration of the KT2 spectrometer (Lawson et al., 2009a). The measured and modelled line intensity ratios of a number of Na- and Li-like metal doublets are compared allowing their relative sensitivities to be found at the doublet wavelengths. Where pairs of wavelengths overlap, the calibration can be extended to shorter or longer wavelengths. As with the KT2 calibration, this procedure has resulted in a particularly accurate calibration, which in the present case extends throughout most of the spectrometer's wavelength range. In addition, it has been possible to use comparisons of measured and modelled CIV line intensity ratios to provide a check on the derived calibration and to allow the calibration at the longest wavelengths to be improved. The KT7 line profiles are such that weak spectral lines require a narrower integration range than is used for intense lines and the ratio of the integrations made with the full and narrow ranges is derived allowing the calibration to be used to give reliable measurements of weak spectral lines.