PRECISION 

The PRECISION  attribute contains a reference to an array of integer values that represent the defined length or size of the columns in the SQL statement.



There are two general ways in which the precision of a column is calculated. String datatypes, such as CHAR   and VARCHAR, return the maximum length of the column. For example, a column defined within a table as:



location        VARCHAR2(1000)



would return a precision value of 1000.



Numeric datatypes are treated slightly differently in that the number of significant digits  is returned. This may have no direct relationship with the space used to store the number. Oracle, for example, stores numbers with 38 digits of precision but uses a variable length internal format of between 1 and 21 bytes.



For floating-point types such as REAL, FLOAT, and DOUBLE, the maximum ``display size'' can be up to seven characters greater than the precision due to concatenated sign, decimal point, the letter ``E,'' a sign, and two or three exponent digits.

http://docstore.mik.ua/orelly/linux/dbi/ch06_01.htm

SQL> set numwidth 50

SQL> select 1/3 from dual;

                                               1/3

--------------------------------------------------

         ,3333333333333333333333333333333333333333

SQL> select systimestamp from dual;

SYSTIMESTAMP

---------------------------------------------------------------------------

12/08/2015 09:38:51.937 +02:00