# Normalized frequency in matlab

I have a progam in matlab that generates a linear and quadratic chirp, and now I want to study the frequency components in wvtool. However, I am not able to decode the frquency domain scale "the normalized frequency". The usual process of deviding the normalized frequency with the sampling frequency doesnot provide the desired value. Please refer to the program and image for details.

Fs = 500;
tf = 1;
t = 0:1/Fs:1;
f1 = 10;
f2 = 90;
slope = (f2-f1)./t(end);

F = f1 + slope* t;
F1 = f1 + slope* t.* t;

fres = fs/fft_size; % Bin spacing