I have the 820, not the 810, so I can only help with the general questions.(posted 8177 days ago)Although a real calibration plague would be best, you can probably get by with a home made calibration standard. You will need a white patch, and a dark grey (almost black) patch, which you will then need to read on another calibrated densitometer. The dark patch should be in the range of 1.80.
A transmission patch would be a little harder to make, and I can't locate one to see what typical values are used.
Visual will give you the reading for black and white (at least I think that is correct).
HD-LD is useful for plotting contrast; it takes two readings, and gives you the difference. It is useful for plotting professional control strips (where this is one of the values plotted), but for your use, I don't think you will need to use it. Just write down the readings you get, and do any calculations needed.
Good Luck, David Carper