reply to u/UsefulLength9143 at https://old.reddit.com/r/typewriters/comments/1ruew5h/royal_p_this_isnt_pics_font_is_it/

Looking closely at the slugs with letters, several clearly have a "P" foundry mark which was commonly used in this time period to identify Royal's "Royal Pica" face (see: https://typecast.munk.org/2011/04/24/1964-nomda-blue-book-royal-font-styles/) which was the generic name they gave in their catalogs to this particular pica (pitch) typeface. Similarly a foundry mark of "E" was often used to represent their 12 pitch "Royal Elite" typeface. Surely it's the case that the designer had some other name for this typeface, but I've never seen Royal documents which specify anything other than Royal Pica or Royal Elite.

While it certainly helps to see the rulers on the carriage to doublecheck, one can guess the exact typeface in this instance solely by the foundry marks, though this is not always the case for a wide number of manufacturers.

Generally people are right in asking to see the ruler as the difference in width of slug on a 10CPI and 12CPI machine is on the order of 1/64 of an inch which is incredibly hard to discern visually on photos like these without something to use for scale.