henry copeland:

Soviet system for predicting nuclear war had lots of complex inputs with an arbitrary threshold

His worries about a surprise attack were amplified by “one peculiar mode of intelligence analysis,” a KGB computer model to measure perceived changes­ in the “correlation of ­forces” between the super­powers, according to the review. The computer went online in 1979 to warn Soviet leaders when “deterioration of Soviet power might tempt a US first strike,” the review says. The computer was at the heart of the ­VRYAN system, according to the review, and thousands of pieces of security and economic data were fed into the machine. The computer model assigned a fixed value of 100 to the United States, and Soviet leaders felt they would be safe from a nuclear first strike as long as they were at least at 60 percent of the United States, and ideally at 70 percent. Reports were sent to the ruling Politburo once a month.
- www.washingtonpost.com