On Wed, 19 Apr 2017, Procházka Lukáš Ing. wrote:

> Hello,
>
> do you mean this? - It shows EXACTLY 3 digits after the decimal point:
>
> ----
> \cldcontext{string.format("\letterpercent.3f", 5.8/1.6)}
>
> \cldcontext{string.format(string.char(37) .. ".3f", 5.8/1.6)}
>
> \startluacode
>   context(string.format("%.3f", 5.8/1.6))
> \stopluacode

\startluacode context("%0.3f", 5.8/1.6) \stopluacode

is simpler.

Also see: 
http://wiki.contextgarden.net/Programming_in_LuaTeX#Arithmetic_without_using_an_abacus

Aditya