Extra Extension Holes

This week I have added to my eBay auctions half a dozen Machin cylinder blocks with extra extension Holes.  This is a nice example with two angled margins,  the extra hole is shown in row 18.

What are they and why do they exist? 

Originally these extra perforations were introduced by the the printers as a reference position to aid the location of bent or missing pins. If you would like to see more of these just  type Extra Extension Hole into your eBay search.

On certain values the EEH can be found in one of several positions. They are found in the left margin of the blocks.  Copies can be found either in row 18, 19, 20 or 21. I might add, they are all listed in specialised catalogues and are highly collectable.

The block above with one angled margin (also for sale) shows the extra hole in the position of row 19.