Conceptually, PRX Metrics counts downloads the same way Podtrac does: by logging each downlaod request and aggregating those numbers.
The difference is where the download is being logged from. PRX Metrics relies on counting downloads from PRX servers. Podtrac counts requests that pass through their servers, regardless of where the actual downloaded file is stored. PRX Metrics will count every file we serve. Podtrac will count every file that has been configured to route through the Podtrac service. You should feel free to use both services and compare the results against one another. That’s what we do!
PRX Metrics are also more up-to-date than Podtrac, because we are reporting our counts in real time, without the multi-hour delay you’ll see from Podtrac.