> For codes designed for length 341 (the first length enough to support
> 512 bits of data):
> * correct 1 error = 3 checksum characters
> * correct 2 errors = 7 checksum characters
> * correct 3 errors = 11 checksum characters
> * correct 4 errors = 15 checksum characters
> * correct 5 errors = 19 checksum characters
> * ...
> * correct 7 errors = 26 checksum characters (~ length * 1.25)
> * correct 13 errors = 51 checksum characters (~ length * 1.5)
> * correct 28 errors = 102 checksum characters (~ length * 2)
>
> So it really boils down to a trade-off between length of the code, and
> recovery properties.
>

At the risk of making the proposal more complex, I wonder if it might be
better to support multiple checksum variants?  The trade-off between code
length and recovery seems to be largely determined by the user's medium of
storage, which is likely to vary from person to person.  I personally would
probably be interested in the 51 or even 102 character checksums variants.