Screening data with P4D

  The purpose of P4D is to examine data for possible errors in data entry.
The printing options allow errors to stand out.  Special symbols can replace
ordinary and extraordinary entries.  For example;

The N option replace all numbers with a space.  This permits other diagnostic
symbols to stand out.

Alphabetic symbols all appear as @ signs if the A option is taken.  

  If the PR option only is taken, the data file is printed out, unmodified.