*fix on something
1. the exact location of something distant. (*Typically: get ~; have ~; give someone ~.) I can't get a fix on your location. Where are you? We are trying to get a fix on your radio transmission.
2. Fig. an understanding of the direction of a discussion. (*Typically: get ~; have ~; give someone ~.) I can't quite get a fix on what you're trying to say. I can't get a fix on where you're going with this argument.
fix something on(to) something
to attach something onto something. We fixed a notice onto the broken door so people wouldn't use it. Please fix a label on this package.
fix (up)on someone or something
to become preoccupied with someone or something. (Upon is formal and less commonly used than on.) She seems to have fixed upon becoming a pilot. James is quite fixed on Janet.