As a child, Fuller showed remarkable abilities in mental arithmetic, effortlessly performing complex calculations in his mind. He gained recognition when he appeared on various television shows, astonishing the audience with his lightning-fast mental calculations. One of his earliest notable achievements was when he successfully multiplied two 5-digit numbers (specifically, 37,987 multiplied by 7,235) in just 38 seconds, without the aid of any external devices. This feat was broadcasted on the television show "Record Breakers" in 1981, capturing the attention of the public. Throughout his career, Fuller has continually demonstrated his exceptional mental calculation skills. Notably, he set a new world record by correctly multiplying two 8-digit numbers (namely, 37,987,244 multiplied by 7,235,855) in just 28 seconds during a live event on the German television show "Wetten, dass...?" in 1989.

Fuller's extraordinary abilities extend beyond multiplication. He can perform various complex calculations, such as division, square roots, and cube roots, rapidly and accurately. Additionally, he possesses a remarkable memory, which allows him to recall past calculations effortlessly. It is important to note that Fuller's mental calculation skills are not solely limited to numbers. He can also calculate calendar dates and days of the week with remarkable accuracy, even for dates occurring centuries ago or thousands of years into the future. Despite his extraordinary talents, Fuller has expressed that his abilities are the result of intense practice and training rather than any innate gift. He has honed his mental calculation skills through years of dedicated practice, continually challenging himself to improve.