Wim Klein

Wim Klein is a mental calculator from Netherlands. Employed as a human calculator at CERN, he set a 1981 record extracting a 13th root in 88.8 seconds in Japan.

Competitive mental calculation is governed and measured: the Mental Calculation World Cup, the Memoriad and the Mind Sports Olympiad all run standardised tasks — adding ten ten-digit numbers, multiplying eight-digit numbers, extracting square roots and computing calendar dates — so results are directly comparable across decades.

What separates a documented record from a family anecdote is that someone else wrote it down at the time. Wim's is recorded in published reference sources, with a date and a figure attached, and that is the standard applied to every entry in this index. Where an age or a date is disputed in the sources, this page follows the published record and says so rather than choosing the more impressive number.

Records like this one rarely survive untouched. The age thresholds that define early achievement keep falling as training methods, coaching and access to competition spread to more countries, and each generation of mental calculators reaches the standard a little sooner than the last. Whether Wim's mark has since been beaten is noted above; the achievement itself is fixed to its date and stands on the record as it was set.