This optical goniometer is typically used for contact angle or surface tension tension measurements using the sessile drop and pendent drop methods.

For contact angle measurements one needs to consider the tested materials hydrophobicity/hydrophilicity as well as the solvent's surface tension (higher is more suitable) and the solvent's dispersive vs polar contribution. For these reasons water is typically chosen as the most suitable solvent for most types surfaces that are not highly hydrophilic.  

The following table is a good reference for finding suitable solvents. 

https://www.accudynetest.com/surface_tension_table.html?sortby=sort_st_disp%20ASC

NOTE! The instrument is placed on an open bench without extra ventilation and thus volatile hazardous solvents like methanol, diiodomethane, etc are NOT ALLOWED (contact tool responsible if you have a motivated need to perform such measurements).

For the most extensive studies, look up the OWRK method.