How do you track the state of a variable?

I'm currently rewriting some Objective-C iOS code in a new Swift watchOS part (the former was handed down to me and I'm more comfortable with the latter). I'm trying to understand how exactly this Core Bluetooth peripheral dataends up as a float representing elevation (and the speed too but I'll just tackle elevation for now). NSLogging it before the switch statement still shows its real time height data and the only part of the entire project I see _fCurElevation mutated is is on line 98 which isn't relevant as it's only reached when the user taps "time mode." How would I go about tracking the state of the _fCurElevation float property in Xcode, assuming I'm heading in the right direction in solving this?