While at school he was above average in mathematics and discovered his calculating abilities as well as his faculty in memorizing numbers.
Henning previously tested other calculators, Dr. Ferrol and Gottfried Ruckle, and found Finkelstein to be superior.
In 1937 an article was published that described and analyzed his abilities, with the general conclusion that although he could perform calculations much more rapidly than most people, his thinking processes seem to obey the same laws and are not indicative of any unnatural powers.
Also, the correctness of the results was not always 100 per cent, decreased rapidly with the growth of the number of "acts of attention", and apparently depended on concentration.
[1] After failing to secure himself a job that matched his abilities and unwilling to become a stage calculator, he attempted a career playing chess between 1941 and 1949.