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
Salter	['sɔ:ltə]
Jocelin	JAHS-lin, JAHS-ə-lin	English (Rare)
Abraam	-	Biblical Greek, Georgian
VÜSal	-	Azerbaijani
Boston	['bɔstən]
Bittor	-	Basque