Hello my fellow learned forum-members,

I won this recently.


** expired/removed eBay auction **


And it is the same as my existing first print, including the blue card of charts... except it has slightly darker blue lettering on the cover and the paper is a little bit stiffer/heavier.  

What do you reckon?  My thinking is that it is a 1st printing variation, i.e. that the first printing run may have been a few thousand copies (2,000 at a guess, maybe more), and at some point during that run they changed ink and/or changed paper stock. I have a friend who does quite a bit of small run printing (photo calendars etc..) and he finds that it is not uncommon to switch paper or ink during a print-run - especially if you are doing it on a budget, as they were in the mid 1970s. Happy to hear any thoughts?

By the way, for comparison here is a 2nd printing:


** expired/removed eBay auction **