On Mon, Feb 10, 2020 at 10:18:48PM +0100, Emanuel Berg via Users list for the GNU Emacs text editor wrote:
> What's this?
> 
>     (- 2.8 1.6) ; 1.1999999999999997
> 
> With the TI-84 Plus,
> 
>     2.8-1.6=1.2
> 
> Normally I'm all pro-Lisp but here...

Those numbers aren't exactly representable as binary fractions
(2.8 = 14/5, 1.6 = 8/5). So things like this happen. It's not
Lisp, but an artifact of the underlying representation (as
binary "floats" with limited precision).

Cheers
-- tomás