EXFO FTB-2 - Manual (Page 266)

Maintenance
256 FTB-2 and FTB-2 Pro
Cleaning the Touchscreen
Cleaning the Touchscreen
Clean the touchscreen with a soft, non-abrasive cloth, such as one used for
cleaning reading glasses, dampened with water.
When not using your unit, EXFO recommends using the screen protector
that came with it.
C
AUTION
Using anything else than water can damage the special coating
used for units equipped with an outdoor-enhanced screen
(S2 option).