I am the author of this question, Bogumił Kamiński helped me solve the problem, however, I changed computers, I am using MacOs and when I went to reproduce the example, I couldn't.
this is my code in the julia environment:
julia> setprecision(BigFloat, 20)
20
julia> x = big"1.23456789"
1.0
should be 1.2345676
and not 1.0
.