I'm building a copy of happy hacking. But I couldn't find clear source of It's dimension.
The only one source I found is this layout-editor format from deskthority wiki (
https://deskthority.net/wiki/HHKB_Professional2).
// simplified
["","","","","","","","","","","","","","",""],
[{w:1.5},"","","","","","","","","","","","","",{w:1.5},""],
[{w:1.75},"","","","","","","","","","","","",{w:2.25},""],
[{w:2.25},"","","","","","","","","","","",{w:1.75},"",""],
[{x:1.55},"",{w:1.5},"",{w:6},"",{w:1.5},"",""]
It specifies the bottom row has 1.55 unit, blank area on left side, which means 'Q' and 'Alt' key dose not vertically aligned, but 'Alt' is 0.05 unit(0.9525mm) shifted to right. As far as I see my HHKB, I don't see such a gap. I'm not sure because I don't have proper measurement. Sub mm distance is really hard to catch with plastic ruler.
Should I trust deskthority wiki, or assume its just typo of 1.5 unit?