Analyzer: Queue Length vs Avg Busy Queue Length

Can somebody explain the difference between the two? They sound like the same thing in the Navisphere Anayzer guide. Also, is there a rule-of-thumb in using one of these metrics to identify bottlenecks? I've read you should keep the LUN Queue length value less than the number of disks in the LUN ("EMC Analyzer: A Case Study) or each disk's Average Busy Queue Length between 1 and 1.5 (Analyzer admin guide).

Queue Length (D/S/L): The average number of requests within a certain time interval waiting to be served by the component, including the one in service. An (average) queue length of zero indicates an idle system. If three requests arrive at an empty service center at the same time, only one of them can be served immediately; the other two must wait in the queue, resulting in a queue length of three.

Average Busy Queue Length (D/S/L): Average number of requests waiting at a busy system component to be serviced, including the request that is currently in service. Since the queue length is counted only when the component is busy, the value indicates the frequency variation (burst frequency) of incoming requests. The higher the value, the bigger the burst, and
the longer the average response time at this component.