Article date: Apr 1967
Article title: The amazing feats of professional mental calculators, and some tricks of the trade
Mathematical Games column? Y
Book: 7. Mathematical Carnival
Chapter: 6. Calculating Prodigies
This data confirmed? yes
Notes
Peter Rowlett (27 August 2022):
Peter Rowlett initial guess (Uncertain)
Peter Rowlett (29 October 2023):
I have seen this chapter and column side-by-side and they match.