The Sadelco DislayMax 800 signal level meter makes 43 measurements across the channel and diplays the average of all readings. If one of the 43 measurements is below -20 dBmV, the meter says "Ur" for under range and doesn't give a reading. The scan covers about 5.3 MHz of the 6 MHz channel.
If the meter is switched to the single frequency mode, it will measure down to -35 dBmV at the center of the channel, but the correction for a digital signal is not added; +6.8 dB IIRC.
The screen on the meter actually shows a dark gray image on a dark green background and doesn't have much contrast. The image looks pretty good on a computer screen, but makes a muddy image on a print.
analog channel:
digital channel:
To make an image that has more contrast and room for notes, I set my digital camera for a B&W image, and then edit in Photo Gallery to increase the contrast.
Photo Gallery will only allow me to increase the contrast one time, AFAIK, so I use Lunapic to increase the contrast 4x more: