Thermo Scientific Microm HM355S Operation Manual page 61

Working with the Microtome
Sectioning Instructions
The knife/blade must never be placed on an angle that is too flat since
the knife/blade does not cut into the block at all this way. Only the rear
side slides over the sectioning surface.
An angle, which is too steep, is also unfavorable as the knife/blade
might vibrate too much while sectioning. The so-called "chatters"
appear on the block surface as well as on the sections as parallel stripes
having negative effects on the microscopical evaluation.
Thermo Fisher Scientific Operation Manual HM335S 61