Numeric Precision - Take a Big Byte?
As Cody & Pass say, "there is considerable controversy concerning the appropriate length of SAS numeric variables."
One possible rule:
Store all numbers in 8 bytes
The advantage of this is the machine always stores numbers in the full precision that the machine can muster; You can do no better than this in terms of precision.
The disadvantage of this is that you may be using more storage space than necessary; You may be able to use less disk space.

The rule for BIOS524:
Don't loose precision but store all variables in the smallest number of bytes.
In particular:
Store character variables with a length of the longest character value.
Store numeric variables whose values are not integers in 8 bytes.
Store integers in the number of bytes indicated in the table, above.
Store dates in 4 or 5 bytes (they are integers).