Precision optical instrument for measuring the intensity and wavelength of spectral lines and for determining the refractive index of a prism. The unit is mounted on a stable base with attached collimator and rotating telescope platform. Features include a 26-mm achromatic optical system with a 10× Ramsden eyepiece and crosshair, a 16-cm-diameter enclosed circle graduated from 0 to 360° in one-half degree increments with a double-ended external 0–30 × 1' Vernier with 2 built-in scale magnifiers, 8-cm-diameter stage with engraved ring pattern, and a 6-mm-tall slit with width adjustable from 0–2 mm. Includes a 25 × 25-mm equilateral prism, 600 lines/mm diffraction grating, detailed instructions, and storage box.