You're right. The tension bar applies a constant torque which is always there. It simply adds to the torque from the dropweight (which is by far greater).
I just meant that, I neglected that part when I wrote down the equation using the dropweight as the sole source of pulling force.
Indeed, it does not introduce an error in the actual stringing of the racquet.
"Physics is like sex: sure, it may give some practical results, but that's not why we do it." -- Richard P. Feynman