Doublet letters in business writing language of the Baikal region in the 18th century

The article reviews one of the notable features of Russian graphics of the 18th century in a rather narrow aspect - the functioning of the letters-doublets in regional business writing (based on the written monuments of business writing of Transbaikalia). As a common example of letters-doublets the authors examine the usage of letters ѳ - ф throughout the century. Sustainable use of the letter ѳ in proper names in the documents of the first half of the 18th century is defined, and also variative writing letters ѳ and ф as in proper names and appellative vocabulary in the second half of the century with the subsequent archaization of letter ѳ and primary use of letters ф in the documents of the last third of the 18th century is revealed.