I want to introduce a very affordable perpetual calendar. This is the Raketa Perpetual Calendar made in USSR. It is manually wound and you can set the date by pumping the crown when in second position. This particular watch is from the early 1980s. In essence this watch has an algorithm on the dial which allows you to calculate the weekday of any day of the year with a quick look. Ill explain how it works below.
The crown at the 4 hour position rotates the outer ring which has the years 1980-2000 on the bottom of the dial and the weekdays on a second ring at the top. On the lower half of the dial you find the months, on the top the dates 1-31.
Here is how it works. Suppose we want to know what day the 7 May 1990 was. We rotate the year/weekday wheel so that the year corresponds to the month column on the dial. 1990 corresponds to may now.
As a result the weekday on the top ring (the black weekday is Sunday) corresponds to the appropriate date, In this case Monday=7th. Since the years only go to the year 2000 you might think the watch is useless now. However, year-day constellations repeat themselves. As it so happens 1990 has the same days as 2018 which means the watch is still perfectly usable.
The russians call these "college watches" because they were affordable watches for students. They are still very affordable and there are a lot of them available. However, true to typical Soviet quality its increasingly hard to find one in very good condition since it pretty much will dissolve instantly when it touches a drop of water.
PS: I love this dial, even the Roman numerals that desperately try to put some class over a really cramped dial which only makes the look more confusing. What do you think?