Torch H2/O2 ratio for ideal combustion?

As long as we’re talking about H2 torches…

Anybody know what the ‘right’ H2/O2 ratio should be on the
regulators for ideal combustion?

I inherited the H2 torch I’m using at school, and never really had
the full rundown on it. I just set the output on the regulators to
20 & 20, and mix by ear. It’s worked fine for 10 years, but it’d be
nice to know what I should be doing…