The waveform mode uses the CRT etched graticule, which requires external lighting to see the graticule. Gamut and Vector modes use an electronic graticule, which does not require the external lighting, so the default is to turn off the scale illumination. Scale illumination can be turned on if desired by pressing the CRT button, then turning the knob under SCALE in a clockwise direction. This will then have the waveform scale in the background as well as the electronic graticule, which can lead to some confusion by the operator.