The brush hand rests on the the mahl stick to give it control and to keep it from touching the wet paint.
My plein air mahl sticks are made from metal or wooden dowel rods. But in the studio I use a 26 inch section of a wooden yardstick instead of a dowel. It is sanded and finished with tung oil.
On the underside of the tip is a wooden spacer. This holds the stick at a constant height of about ¾ inch above the paint surface. The inside of the tip is hooked so that the mahl stick can hang vertically onto the top of the drawing board when not in use.
The yardstick markings make it handy for measuring and for ruling lines in the pencil stage. Wood-burned into the top surface is the classic maxim from Ovid: “ARS EST CELARE ARTEM” (it is art to conceal art); in other words, "true art conceals the means by which it is achieved." You might find another maxim that fits you better at this link or this link.
From time to time I use an acrylic bridge. This also stands about ¾ inch off the drawing surface on two legs. This is especially good for inking with a dip pen or Rapidograph.
Tomorrow: Color—from Mask to Palette