-1/12: Answer from My Imaginary Calculator
These days, input systems based on prediction are common, even for werstern world. Perhaps, because of phones.
It would be interesting for a calculator to adopt "prediction" feature, I considered.
Then, the temporal output for input: $1+2+3$ is $-1/12$, before pressing '=' key?
P.S. When my friend is teaching math in India, I am reading about Ramanujan. And I'm a fan of Euler.