I got this conceptual question. I'm still feel kind of stuck in btw of something, but I don't know what it is.

Suppose I have a cathode-ray tube (shown in the pic):

http://img189.imageshack.us/img189/5839/001ute.jpg
, with Vz (I replace the 2 with z for typing purpose) be the accelerating voltage, Vd be the deflecting voltage taken from the DC power supply. I'm firstly ask to find tanθ and after all works, this is final formula for tanθ:

http://img193.imageshack.us/img193/5095/002gmo.jpg *Now, the question is this: If I'm gonna plot a graph of tanθ vs Vd, what does the slope of that graph represent?*
My interpretation is that tanθ is the rate of deflection that the deflecting electrical beam "shoot" to the screen, or in short tanθ = D/L geometrically. Also, l/d is the vertical deflection of the plates

And base on the derived equation of tanθ that I got, the slope of tanθ vs Vd should be equal to (l/d)(Vd/2Vz). Talking as a whole, what will the slope: (l/d)(Vd/2Vz) actually stand for?

Please help me out, I'm currently have no lead to get this problem done >_<