Now approved by NIOSH for use in the USA. 4 band is no longer available. This is a Mark III version.
The slide provides a means of checking the detection limit of phase-contrast microscopes and is intended primarily for use with the membrane filter method of measuring airborne asbestos fibers.
Daily use of the Phase Shift Test Slide (5 Band) is required in Britain during measurement by the European Reference version of the membrane filter method.