The reason for it was the ability to label each card with a number. One didn’t have to; labels were used for the dreaded “go to” variously conditional branch statements as a necessity, but most of us who wrote much code learned damn quick to get a sequence number somewhere on the card. Lines 73-80 were also used for that, but it was a honkin’ PITA to get to column 73 on a keypunch.

If you doubt the need, consider that one Fortran/assembler program I wrote required enough 2000-card boxes of cards that I had to haul them to the comp center with a wagon. A biggish wagon. Now hit a bump with the wagon…

The Fortran 77 syntax requires that you give 6 spaces before any commands. These 6 spaces originate from the punched card version of Fortran. After the first 6 spaces, you may place additional spaces for indentation if you wish.

However, there is a maximum total line width of 72 characters (including the first 6 spaces). If you require extra space you can put any character (except 0 with some compilers) in column 6; this is called a “continuation character”. With punched cards, this meant that you could continue the line onto a second card.

One time I wrote a FORTRAN program and I could not for the life of me figure why it wouldn’t compile. Took it to the student instructor and he couldn’t figure it out for the longest. Finally he realized that I had too many spaces leading the code. If I remember correctly you had to have 6 spaces, or maybe it was 7, and then start on the next space. Don’t ask me why I just remember you had to punch in spaces(it was a long time ago). I had one too many and it would just throw up and tell me nothing.

Touché.