In my limited world the ISPF EDIT command HEX accepts the two parameters ON and OFF. Then one day someone broadened my horizon by using the parameter DATA. Normal editing of a dataset or member is in mode HEX OFF. To see the HEX values you use ISPF command HEX ON. As you know, you now have two extra lines of data for each record. The first extra line shows the value in hex of the first halfbyte of the original byte and the next extra line shows the last halfbyte in hex.
The way that the HEX ON screen is build is easy to understand, but sometimes it can be difficult to read and edit in the hex values when you are dealing with a string of hex values. In these cases you have to split the byte string and place every second hex value in the top line and the other in the bottom line. With HEX DATA this problem is no problem any more. Imagine this display of a record 14 bytes long in HEX ON:
After issuing HEX DATA it looks like this instead:
Now it is much easier to see that the last four bytes is a date in DB2 internal format. Another result is that the one to one correspondance between the bytes in the original record and the hex representation is gone with the wind. Editing of the date in the hex part is much easier, though.