If you understand Russian handwriting you can read original design from my notes from April 1994:

At that time it was 1 extra button "agree", but now I decided to remove it to make process of entering faster - anything wrongly entered always could be deleted by "backspace" code.

And at that time I also thought about RF way to deliver codes to computer as if it was Bluetooth already available ( it was not ; )

Somewhere around 2000 I even wrote a simulator for PC when you can use some keys of regular PC keyboard to mimic this chorded keyboard, but unfortunately I lost both sources and binaries of that program, so I'm going to write a new one...