[en] A scanning visible spectrometer has been prototyped to complement fixed-wavelength transmission grating spectrometers for charge exchange recombination spectroscopy. Fast f/1.8 200 mm commercial lenses are used with a large 2160 mm-1 grating for high throughput. A stepping-motor controlled sine drive positions the grating, which is mounted on a precision rotary table. A high-resolution optical encoder on the grating stage allows the grating angle to be measured with an absolute accuracy of 0.075 arcsec, corresponding to a wavelength error ≤ 0.005 (angstrom). At this precision, changes in grating groove density due to thermal expansion and variations in the refractive index of air are important. An automated calibration procedure determines all relevant spectrometer parameters to high accuracy. Changes in bulk grating temperature, atmospheric temperature and pressure are monitored between the time of calibration and the time of measurement to insure a persistent wavelength calibration