This compact Australian-made direct vision Spectroscope by IEC is a very useful hand-held 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.
A useful PDF file introduces the principles and explains Angstrom units, nanometres, the spectrum and much more.

Instruction Sheet included