What I do and what the web guys did is transcribe an existing document. No reason to do anything but copy what is there.
HOWEVER, if it is a living document, a manual of procedure, etc, there is much more reason, so long as you don't want it to be an epub.
HOWEVER, why should it be an epub and subject to reflow in the first place when it is easy to create PDFs which have no such problems and which is a heck of a lot less work.
I just wish the standards people and adobe were more interested in getting work done and accommodating existing documents than creating standards which are not supported in the real world.
Thanks, I will try the ideas for centering. I will just try to ignore the other checkers which are finicky about what they will accept but which play fine on most devices, since I have no interest in commercial publishing.
I will probably put the two books I have been working on up to MR in today after fiddling with centering. One has a table that will take a microscope to read, but there are no such things as fold out screens, yet anyway.