Hello nikalk,
Centova Cast's listener graphs display the total number of distinct listeners (not simultaneous listeners) in a given hour. So for example, if one listener tunes in, then disconnects, and then another tunes in a few minutes later, this is considered two listeners.
We feel that the hourly distinct listener count is a more valuable metric than hourly simultaneous listeners, given that you already know the maximum listener limit for the stream.
Regards.