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
Ctirad	-	Czech, Slovak
Sung-Min	sung-meen	Korean
Irvin	UR-vin	English
Katarina	kah-tah-REE-nah (German, Swedish)	German, Swedish, Norwegian, Danish, Hungarian, Croatian, Serbian, Slovene
Conner	KAHN-ər	English (Modern)
Leontiy	-	Russian