For anyone interested in gaining a better understanding of the evolution of A.J. Parker/Parker Hale micrometer sights, I'd recommending locating this rare and interesting book called
A Century of Sights and Sighting Aids by Edna Rosalind Parker. She is the daughter of Alfred J. Parker (founder of Alfred J. Parker Ltd.) and granddaughter of A.G. Parker (founder of Parker hale Ltd.). With her knowledge of the business and access to all of the various historical documents and pictures of the various sights, this little book makes for a very through and accurate reference piece on the subject. There is no ISBN number for it, so I'd suggest you use a "Google" search on the title to see if you can find a copy from one of the rare used book sources on the Internet. I found my copy on a table at a local gun show.
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