Are you generating the font in TrueType?
Because every time you go PS to/from TT
points get added (to approximate).

hhp

yes, that was the problem. i tried to export in opentype and the points remain the same.
thank you very much Hrant

I still don't know what is the best format to export a font...I'm a beginner.
(suggestions are welcome)

In terms of curve definitions, there are two: cubic (PS)
and quadratic (TT). Most people design in the former, but
most actual fonts end up in TT format. Ideally you design
in the same curve definition model as the output format,
but most people never get comfortable (or bother getting
comfortable) designing in quadratics.

hhp