A man who challenged crowds to stump him with maths problems was one of the highlights of Brisbane's very first Ekka, according to a new book.

The mystery entertainer has been dubbed the "Rain Man" of the 19th century by the authors of a book on the 132-year history of the Brisbane Ekka which is due for release next week.

The Rain Man earns his name from the 1988 film starring Tom Cruise and Dustin Hoffman in which Hoffman played Cruise's older, autistic brother, who staggered people with his maths knowledge.

In 1876, the real identity of the man dubbed "The Lightning Calculator" remains unknown, but history records him as one of the true pioneers of vaudeville entertainment at the inaugural Ekka.

Authors and historians Joanne Scott and Ross Laurie tell the story of "The Lightning Calculator" in their book Showtime: A History of the Brisbane Exhibition , to be launched at the Museum of Brisbane on July 25.

Scott, now an associate professor of history at the University of the Sunshine Coast, said the man was a genuine crowd pleaser for his time.

"Apparently he stood in front of the crowd and did these amazing mathematical sums in his head," she said. "That was 1876, at the very first show.

Laurie said the man was like the "Rain Man" of his time, performing staggering maths sums continually.

"He would just come out with the answer, like the square root of 95 or something," Mr Laurie said.

"But there is no more detail than that, or even if he ever performed again." Associate Professor Scott said the man was certainly part of the early days of the Brisbane Ekka when 17,000 of the 22,000 people who lived in the city in the late 1870s would come.

"He was part of the noise and crowds and colour and was part of that very first part of that daytime entertainment."

Other fascinating facts contained within the pages of the book about the RNA is a 1954 statue of Queen Elizabeth II made entirely from butter.

Mr Laurie said the lifesize image was sculpted by local artists Len and Kathleen Shillman as an advertisement for the Queensland Butter Board.

"They hired these two local sculptors to do lifesize advertisements. So for the Royal Tour (in 1954) they did the Queen," he explained.

"Previously they did Winston Churchill and they did the Melbourne Olympics (in 1956).

And yes, the models were kept in refrigerated cabinets.