Regarding the bi-focals,
I too, had a similar pair made up by an optician friend, called an
"Executive Bifocal", and they are terrific. I have them set up in a
wire frame, polycarbonate lenses, with a scratch-resistant coating.
My prescription is on the top, and a 2.50 add below for a 12-13 inch.
working distance. The division line is just about midway on the
lense. I have great magnification at the bench, and when I look up, I
have my normal distance vision around the studio. The plastic lenses
are going to be the way to go over glass lenses, as the glass ones I
had made at first were so heavy they slid down my nose.
The size of the lense makes for effective safety glasses, as well,
so I don't have to worry about working with the flex shaft or
buffers. I'd never go back to a "head-band" type of magnifier.