def PA():
    Lx=640; Ly=480; F=8; 
    Lx2=int(Lx/F); Ly2=int(Ly/F)
    X1=int(Lx2/8); X2=X1*2; X3=X1*3; X4=X1*4; 
    X5=X1*5; X6=X1*6; X7=X1*7
    XX1=X1*F; XX2=X2*F
    XL=X2; XR=X6; 
    return Lx,Ly,F,X1