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
Evgenija	-	Macedonian
Williamson	['wiljəmsən]
Ivane	-	Georgian
Mikhailu	-	Old Church Slavic
Armazi	-	Georgian Mythology
Ludo	-	Dutch