How to find Hit Ratio Buffer Cache in Oracle Database

This script is of good use when trying to improve the Database Buffer Cache. 

select (1 - (sum(decode(name, 'physical reads', value, 0)) /
       (sum(decode(name, 'db block gets', value, 0)) +
       sum(decode(name, 'consistent gets', value, 0)))))
       * 100 "Hit Ratio Buffer Cache"
from   v$sysstat;

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