HP Scitex FB950 Printer series - Manual (Page 95)

Clean media thickness sensor roller (quarterly)
Debris on the media thickness sensor can result in inaccurate measurements. Clean the roller to keep
the sensor operating correctly.
▲ Using a lint-free cloth that is saturated with IPA (isopropyl alcohol), clean the media thickness
sensor roller by manually turning the roller with your finger while applying the cloth to the roller
surface.
ENWW Clean media thickness sensor roller (quarterly) 89