Numeric field parameter exact value

Hello,

I am trying to understand why I cannot enter a precise value into my field parameter.

I need to enter eg 320.000 into input box but I end up with 320.200

To make it work I need to play with different increment values but then some other value cannot be entered again.

field paramterer definition -->"IlośćTuszki = GENERATESERIES(0, 500000, 50)"

 

That value exists in the auto generated series.

This is really frustrating, what am I missing here?