Okay, I get the confusion here. This code could be more clear but here's the breakdown:

- There are two groups of metrics that Librato accepts: Gauges and Counters.
- When submitting a JSON payload of metrics metrics must be collected in an array as a value of a hash named "guages" or "counters".
- Line 54 grabs a pointer to (creating, as needed) that metric's correct hash (aka `NSMutableDictionary`)
- Line 55 adds the metric to the dictionary