[oracle-l] Index block count

I have a b-tree, unique, local, prefixed, range partitioned index.  The blevel
on all of the partitions is 2.  There are no chained/migrated rows in the table.
 
I have a query that selects 1 record and only uses the index.  I am not sure why
the query uses 4 blocks.  I would think that it would just have to use 1 for the
branch block and 1 for the leaf block.  Can someone explain it to me?  (I have
run the query 8,000 times and the average blocks per execution is 4.1)
Thanks,
Tom

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