Set of nine slides in 50 x 50mm mounts, six of them having a series of slits, numbering from 1 to 6, each slit approximately 0.0625mm wide and separations between slit centres of 0.25mm
The other three slides are coarse gratings with the following features:150 slits with the same width and separation as the multiple slits above.150 slits, half the width but with the same separation.300 slits, half the width and half the separation
