How to adjust the accuracy of a Vostok Komandirskie
Those Vostok watches are pretty good for their price i got mine for about 50-60€ from ebay and it has been working great. Even though are not famed for their accuracy they are pretty durable, with a service interval of 10 years compared to 3 that most manufacturers suggest. It is said they are the watch equivalent of the AK47. Mine was working well losing just a few minute per month, until suddenly it started losing 30-40 minutes a week! To be honest i did bang it a few times while wearing it (if you get one be careful of the glass, it scratches easily).
Let me start by saying that i am in no way a Professional watchmaker, i am just an amateur trying to adjust his watch. It turned out way easier than expected. To open the caseback i used calipers to grip the sockets of the ring and unscrew it. By the way the design of the caseback is ingenious, the separate ring and backing allow for a better seal without risking tearing the o-ring and the letters are always aligned. To measure the accuracy watchmakers use machines like the one on the left and they are not cheap (~100-200€). Fortunately there is an app (Watch Accuracy Meter) that uses the phones microphone to do the same thing, It might not be perfectly accurate but it will work just fine.
When measuring there are two numbers that interest us, one is the beat error that should be under 0.7s and the other is the beat rate that should be as close to 0 as possible. From my understanding getting it exactly to 0 is not possible because the rate also changes depending on the orientation of the watch. Once you open the watch you will see two levers that you can adjust, one is for the rate and the other for the beat. I would recommend adjusting only the rate as i have not tried to adjust the beat because it was not needed in my case.
Be very careful while it is open not to drop anything inside, even a small hair can disturb the balance of the delicate mechanism. One wonders how such a beautiful feat of engineering was made by hand in the old times. To adjust the rate you only have to move the rate adjustment lever very very slightly towards the plus or minus depending on if you want it to go faster or slower, you can use a toothpick or a plastic spudger just be careful not to disturb the delicate spring bellow. You might have to do this process a few times until it gets close to zero. After doing this to my watch the error rate improved significantly, it is going ahead about 1 minute per week (i should probably have another go at adjusting it).