The IEC compact Direct Vision Spectroscope is a very useful device for measuring the wavelength of light. An adjustable slit allows the light to enter the black chamber and the viewing eyepiece carries a 600 line/mm grating. The eye sees the incoming light split into its colours or wavelengths that appear to be deflected to the right hand side. The coloured bands appear over a scale calibrated in nanometres (nm) with each digit on the scale representing 100nm.