I set drag by feel, not using any sort of machine or scale.

All my swimbait reels are Calcuttas or Calcutta TE's. I set them the night before. This makes up for the fact that I am usually half-asleep in the morning and likely to forget to set my drag. The way to set them the night before is as follows:

With the drag tight, pull off 30 or 40 feet of line
Reel the line back on with good tension using your thumb + forefinger
Back the drag off
Tighten the drag up and pull on the line
Adjust the drag
Always set the drag by tightening it to the point you want
Never back the drag off to where you want it and leave it

Drags expand and contract with temperature and humidity and such. Always check the drag before the first cast in the morning and occasionally throughout the day.

Oddly (and there is probably some technical reason for this) the higher end round reels with multiple drag washers will tend to 'self-adjust' more than say a Curado which has only 1 drag washer.

When you fish you will have tension on the line so there's usually no need to strip line off and wind it on tight before setting the drag.