"This item is not returnable"
*** Effective immediately, the 4 Band Phase Shift Test Slide has been approved by NIOSH 7400 & HSL. There is no time-table when and if the 5 bands will be available.
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.
The test objects on the Mark II version, which is commercially available, are sets of ridges of resin, mounted on a conventional microscope slide, and immersed in a second resin of slightly lower refractive index. The finest ridges are too faint to be seen by most good-quality microscopes. The great majority of users who responded to inquiries found the slide a useful accessory.