So you want to use `bc` for some hexadecimal maths. You set the input base:

ibase=16

and the output base:

obase=16

Oops! I just set it to output in base 22. I’d already set it to think numbers were *input* in hexadecimal, and that’s how it handled the “16” in my `obase` command. Either do this:

ibase=16 obase=10

Or this:

obase=16 ibase=16