have a fix on (something)

To have a firm, clear understanding or determination of something. I hope everyone has a fix on the material, as you'll be tested on it next week. I thought I had a pretty good fix on English idioms, but I don't understand this one at all!

Common Names:

Name	Pronounced	Usage
Kasi	-	Indian, Telugu, Tamil
Korbin	KAWR-bin	English (Modern)
Marc	MAHRHK (French)	French, Catalan, Welsh
ThỊ	-	Vietnamese
Nash	NASH	English (Modern)
Nazario	nah-TSAH-ryo (Italian), nah-THAH-ryo (Spanish), nah-SAH-ryo (Latin American Spanish)	Italian, Spanish