This is "Memoria Technica for Numbers," is a technique that Lewis Carroll devised to help remember difficult numbers. He made several copies to send to friends and colleagues, and used his new Parker electric pen to do it. In those days, before even the invention of carbon paper, it was difficult to make copies, and many companies looked for solutions, with various degrees of success. Often copying processes were so laborious and expensive that businesses found it cheaper and simpler to employ clerks whose job was to copy all the correspondence out by hand.

This pen, designed by that genius Edison, worked by pricking holes in the paper and rubbing ink into them. Carroll bought it on 20 June 1877 He used it it to produce many duplicated items to circulate among his friends. The British distributor of the electric pen, The Electric Writing Co. Ltd., published this testimonial from Dodgson in their edition of the electric pen instruction manual:

July 11th, 1877
I have tried the new Electric Pen for writing MS, printing and drawing, and consider it perfectly successful for all three purposes. For simplicity, expedition, and cleanliness in working, it seems to me to be quite unrivalled, and those who, like myself, often require twenty or thirty copies of questions or formulae, &c., will save the cost of the machine in printer's bill several times over in a year.

Mathematical Lecturer of Ch.Ch., Oxford

The letter is dated only a few days after he bought it, and one imagines him being so delighted that he wrote his letter right away, rushed out and posted it. I hope it proved reliable and he continued to like it so much.