You would pass the number of schedules to 'getAvg' (or possibly the the constructor of 'Buckets') because this should be constant across the graph.
The other thing that might make sense would be to return a total rather than an average. The main problem with my idea is I'm not sure what to do about cases where no data appears, like if data wasn't being collected or was turned off.
Anyway I hope you can see how this is a potential problem.