about the features_l.csv

[hluler]

hi , when check the client.py, the features_l.csv is missing, and
X = [float(realdata[k][1]) for k in range(i,i+50)]
Y = [float(realdata[k][2]) for k in range(i,i+50)]
Z = [float(realdata[k][3]) for k in range(i,i+50)]

MAG = [float(realdata[k][4]) for k in range(i,i+50)]

what is the realdata[k][4] mean?