I apologise if this has been addressed before but I cannot find anything on it.
I have updated my kindle 3 to the new v3.4 firmware but have family members that have older Kindles. I would like to produce ebooks that can be read on all the devices. I think they are call combo files i.e. I understand that the Kindle reading device would select either the old MOBI or the new AZW depending on what it can understand.
Can someone tell me what settings I have to change in Calibre to get the new combo files into one book and also what extension would result?
Thank you