Numworks - Question about frac()

[Pälzer]

Hello,
in the office I use the calculators HP48sx, HP19b and another Casio 4000p (fits so nice in the shirt pocket).

HP48sx:
Input: "4.15" [FP] Display: "0.15"
Input: "-3.95" [FP] Display: "-0.95"

now I accidentally made the input with my seldom used Numworks:

Input: "frac(4.15)" Display: "0.15"
Input: "frac(-3.95)" Display: "0.05"

are FP and frac() 2 different commands?
I am confused.

(Please don't hit me right away, I only had 2 years of math (algebra) as an elective in school).

Thank you