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
Ronaldo	-	Portuguese
Aisha	-	Arabic, Urdu, American
Raye	[rei]
Thurstan	THUR-stən	English (Rare)
Aulis	OW-lees	Finnish
Ruaridh	-	Scottish