The Call Rates chart shows the rate at which various events are occurring in SQL Server. This information will give an idea of how busy the SQL Server is at any time.
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The following statistics are charted:

Batches

shows the rate at which clients are issuing batches of SQL statements to SQL Server.

Compiles

shows the rate at which SQL is being compiled into the procedure cache. Note that this figure includes Re-Compiles.

Re-Compiles

shows the rate at which SQL Server is re compiling stored SQL in the procedure cache.