about length of a numeric varaible in dataset

[kwu]

when I define a numeric variable (or attrib) in a dataset,and try to insert a value greater than 2500k, it starts having the round off error, SAS does not complian the overflow (no warning or error) but just insert it with round off error.
I am trying to understand how sas stores the numeric value with different length and how to calculate the safe data range for a specified length? which doc?

I checked in the help and find that I can add a check constraint. I wonder how much overhead it is when adding this type of constrain to a table? Would it be more efficient by checking the cloumn in the code before inserting the data into the dataset ?

Any suggestion would be high appreciated.

[chang_y_chung_hotmail_com]

See this sas-l posting and the link in it.
http://tinyurl.com/2c8939j or
http://www.listserv.uga.edu/cgi-bin/wa?A2=ind1009C&L=sas-l&D=1&H=0&O=D&T=1&m=291216&P=11759