How to calculate average time for consistent read block requests for the instance in milliseconds?

How to calculate average time for consistent read block requests for the instance in milliseconds

Global Cache Block Transfer Rate=(gc cr block receive time * 10) / (gc cr blocks received)


SELECT
 gc_cr_block_receive_time AS "Receive Time",
 gc_cr_blocks_received AS "Blocks Received",
 (gc_cr_block_receive_time * 10) /
 gc_cr_blocks_received AS "Average Latency (MS)"
 FROM
 (
 SELECT value AS gc_cr_block_receive_time FROM v$sysstat
 WHERE name = 'gc cr block receive time'
 ),
 (
 SELECT value AS gc_cr_blocks_received FROM v$sysstat
 WHERE name = 'gc cr blocks received'
 );

Sample query output: 
Receive Time            Blocks Received                            Average Latency (MS)
------------              ---------------                               --------------------
5305                        2179                                              24.3460303

Julian Dyke - "Pro Oracle Database 10g RAC on Linux" - p692
"The latency of a consistent block request is the time elapsed between the original request and
the receipt of the consistent block image at the local instance. Using a Gigabit Ethernet interconnect,
this value should normally be less than 5 ms and should not exceed 15 ms, although this can be
affected by system configuration and volume."