Check mainspring weight using a drill press. I use a small light vise like this one,
http://www.micromark.com/quick-jaw-vise-2-1and4-inch-capacity,8093.html
a scale like this one,
http://www.amazon.com/dp/B008D6V2D2/ref=pe_385040_30332200_TE_item
and my drill press with a 1/8" diameter steel rod about 3" long clamped in the chuck.
Nothing special about the equipment - just what I use.
Firmly clamp the fully assembled mainspring housing in the vise oriented with the cap up (normal position). Place the vise on top of the scale and place both on the the drill press table. Adjust the height so that the steel rod clamped in the drill press chuck almost touches the top of the mainspring cap and is centered in the cup in the cap.
Zero (tare) the scale.
For a quick spring check, slowly move the chuck holding the 1/8" pin down until the mainspring cap just starts to lose contact with the mainspring cap pin. A 19 lb mainspring will read about 15 lbs on the scale. A 23 lb mainspring will read about 20 lbs on the scale.
If the drill press has a precise scale for measuring chuck movement, it can be used to measure spring rate by comparing the scale readings at two (or more) different compression amounts and dividing the difference in scale readings in pounds by the difference in chuck movement in inches.
Dividing the measured spring rate by 1.2 will provide the spring weight at 1" (normal) compression. A 23 lb mainspring has a spring rate of about 28 lb/in and a 19 lb mainspring has a spring rate of about 23 lb/in.
Not exactly precise, but probably as close as the spring weight markings on a new spring package.
