Larry Caldwell
Super Member
It actually appears closer to a true sine wave than the Wen, which apparently outputs a modified sine wave that ramps in a linear fashion to max voltage, then ramps in a linear fashion to the negative peak. The hash you see in the YouTube video is not harmonic distortion, it is noise. The only way to measure harmonic distortion is through a Fourier analysis of the wave form. Here is a short demonstration of how to measure harmonic distortion.
FFT Tutorial - YouTube