In the 1960s and 1970s, Jarecki started visiting casinos across Europe and began working with his wife
Carol and others to keep track of tens of thousands of spins of roulette wheels, often over the course of a month. After analyzing the results, Jarecki was able to determine that some wheels had a subtle bias that made it more likely to land on certain numbers due to imperfections and wear, though he created a cover story that he had used a computer at the
University of London to crack the games. He preferred to target European casinos, as they used wheels with 37 numbers (unlike the 38-slot wheels prevalent in the United States) and the casinos there were less likely than their American counterparts to cut off a gambler on a winning streak. After several profitable streaks at the
Sanremo Casino in the late 1960s, its managing director described him as "a menace to every casino in Europe" and hoped that Jarecki "never returned to my casino". Even when wheels were changed, Jarecki was able to recognize the unique characteristics of each wheel by sight. The casinos finally caught on to Jarecki's methods and began switching roulette wheels more frequently and worked with manufacturers to make wheels with finer tolerances that were less likely to have the types of imperfections that could lead to exploitable circumstances for Jarecki. == Later life and death ==