This post at XIX век asked about “a book written to help Soviet-era Russian readers figure out the nineteenth-century realia they found in classic literature – things like how many desiatinas are in a hectare, or what counted as a lot of money to a middling noble family.” That rang a bell with me; I was pretty sure I remembered the same book, and eventually I found I had mentioned it in this post back in 2004. It’s Что непонятно у классиков, или Энциклопедия русского быта XIX века [What we don't understand in the classics, or An encyclopedia of Russian daily life in the nineteenth century], by Yuri Fedosyuk (online here). Here’s an excerpt from a 1959 letter by Fedosyuk proposing what eventually became the book: “Мне, знакомому лишь с метрической системой, неясно, богат или беден помещик, владеющий двумястами десятин земли, сильно ли пьян купец, выпивший „полштофа“ водки, щедр ли чиновник, дающий на чай „синенькую“, „красненькую“ или „семитку“.” [It is unclear to me, who am familiar only with the metric system, whether a landowner who has two hundred desyatinas of land is rich or poor, how drunk a merchant is after drinking a "half-shtof" of vodka, and whether or not an official who gives a tip of a sinenkaya, a krasnenkaya, or a semitka is generous.] It turns out that a desyatina is 2.7 acres, a shtof is about one and a quarter liters, a sinenkaya ['little blue one'] is a five-ruble note, a krasnenkaya ['little red one'] is a ten-ruble note, and a semitka is a two-kopeck coin (presumably a terrible tip). The interesting thing to me is the large number of variants of the latter word; Dahl has семичник, семишник, семёшник, семичка, семак, семиток, and семерка. The fact that he includes them in a “nest” of words starting with семи-, the prefix for семь ‘seven,’ suggests that he took them to be related to that number, but how is beyond my understanding.