There is no ‘fastest’ and best’ mental calculator ever, because there are many different categories. She only displayed one category here. Multiplication.
There have lived more than 100+ billion humans in history. Can you benchmark them all for mental speed? - No. So, I would personally refrain from using fancy words such as ‘fastest ever’ or ‘best ever’.
Ok, I know that Devi had calculated correctly a 13 x 13 (with the second number having a 0 in the end.)
But me, Scott, Jan, Melik, Yusnier and others in Dresden 2014 witnessed a 14 yo Indian boy (Granth) doing a 20 x 20 multiplication in around 2 minutes and 30 seconds.
And I am 100% sure that this 20x20 operation was randomly generated.
But with these TV shows and documentaries, I am not really sure about the neutrality of the chosen question. (Same with the high 13th root of Alexis Lemaire.)
And Granth is not even the best in the world in multiplication. He is just the 4th best ever.
Mental Calculation World Ranking Lists
And since Johnny mentioned Gamm, you can see his results in the link above. It’s all benchmarked.
If you don’t see him on the ranking tables for addition, roots or multiplication, this means he did not finish 10 tasks correctly on time, in any of the competitions that he took part (i think the first 3 World Cups and 1 international Memoriad ('08) .
In my opinion both Marc Sanz and Mrs. Lee (and probably Freddy as well) could easily break Devi’s record of 28 seconds for a 13 x 13 if they wanted. In fact, in the next World Cup, I will ask them to do so, and hopefully record it on video.
The Memoriad software currently allows multiplication generators of 3x3 up to 10x10 and only 20x20 as a special mod, so hopefully there will be a modification to add 13 x 13 as well. If not, I will generate 1 task from online number generators and ask them to calculate the product on the drawing board or write down the product result on paper
Granth has quit competing in the last 7 years, so I am not sure if he still practices.
Also, besides calculation, many other activities which Mrs. Devi did , seem to me of very low intelligence (astrology , tarot etc.) .
Finally, the biopic movie that Bollywood did for Devi, was very mediocre and unnecessarily fixated on drama/romance.
I liked much better the Indian biopic movie about Ramanujan (’ The Man Who Knew Infinity ’ )