Medical surfaces that detect pathogens.
Similar to the bedroom, there was nothing on any of the flat surfaces, not even dust.
In the late seventies and early eighties scaling these challenging surfaces really caught on.
Even if the slide itself is mechanically perfect, the irregularity in the thickness of the lubricating oil between the bearing surfaces of the slide is apt to produce a variable error.
The plates are compressed from before backwards, the anterior and posterior surfaces (as seen in the worn grinding face of the tooth) being nearly parallel.