I have been working to get a Brooks B17 adjusted to the right height, angle, etc., and usually read about handlebar height in relation to saddle height. Question: what part of the bar is usually being referred to? I have drop bars. If someone writes that about handlebars, "at about the same height as the saddle," would that usually mean the tops of the bars? Or just whatever part of the bar you are using? It seems like there is a convention to the terminology because I never see it explained...

It's the tops of the bars (or the top of the stem if you prefer). This is a rule of thumb, so start with that adjustment but feel free to jam your thumb into it if it doesn't feel right. Many tourists find that they like a more upright position with higher handlebars -- after all, they're spending more time on the bike each day than calisthenic road bikers. Adjust, evaluate, decide.

Calisthenic road biker? How did you know I sometimes do arm circles while riding? Seriously, I use the same position on my racing bike as on my touring and mountain bike. It is the position a framebuilder and I determined back in 1978 using the old blue Itialian Olympic Cycling book whose name escapes me (I.O.C.C. ??) . I am 5' 11" and my bars are about one and a quarter inches below the level of the seat. Ride in whatever position you want, but keep in mind the more weight that you take off your hands by sitting upright is that much more weight on your rear end. I don't equate time spent touring with needing a more upright position. You might be amazed at how much time real competetive cyclists spend on their bikes.

Venturi95: Good for you! As I get older my butt is more resilient and my wrists are more fragile, so my handlebars have gone up relative to my seat, and I worry less about the wind resistance.

Anyone my age who can still tuck further down through a long day's tour has my respect and envy!

https://www.sheldonbrown.com/frame-si...andlebarheight

Go to Sheldon Brown's page on bike fitting .
His perspective might suprise you. One thing I took away from reading this is that
the number and method of measurement are far less important than setting the height
to a level that is comfortable to you. Since this is not a low tolerance measurement nor is tightly
correlated to the proportion of one of your body parts. I would simply measure it from the top
of the bar (or the bottom) because that would be easier than the centerline. Then when you right down the measurment to communicate with some one you could also provide the bar diameter and the measurement
location.

I used to have problems with hand numbness. On a tour down the Oregon coast it got so bad that my left thumb went numb and it didn't go away for about three weeks after I returned home. The tops of my bars were about three inches below the top of my saddle. I raised the bars with a new stem to about 1/2 inch below my saddle. That feels right and my hands don't get numb anymore.

I still ride in the drops when there's a strong headwind and I think it helps. So if you want to cut through the wind and go fast, lower handlebars might be an advantage. However, if you want to be comfortable, especially on tours when you're riding significant miles day after day after day, raise the bars to where they feel good, and don't worry about aerodynamics so much.

This is a real tough one. I think bar heighth depends on many things. When I went out for a week or two, I had to lower the bar to ease shoulder pain. Then I remembered that all my long sleeve shirts come from tall person shops, or are 17-1/2 in. neck and 37-38 in. sleeve length. With the tall shirts the tail comes down almost to my knees. With one bike measuring system, this meant that I have a short torso and long arms. When I try to cram these arms into the space that a 34 in. arm goes, it hurts a lot. My bars are about 50/60 mm below seat height. I know there is a fit system that measures the angle of the knee to set seat height, I feel that the angle of other joints is important as well, shoulder, elbow and wrist need to be in a comfortable natural angle to work well.