A little info on load cells. This could be useful for us poor folk here
that may not want to buy a $300 or more scale but have occasional need to
weigh something that we don't have the proper scale for.

Load cell output is normally expressed in millivolts per volt. Most of the
industrial load cells I run across at work are rated at 2 millivolts per
volt, that means if you use a 10 Volt excitation then at the load cell
capacity the output would be 10 X 2 mV or 20 millivolts. So, if you had a
20,000 lb. load cell, and used a 10V excitation, you would get 1 mv output
for every 1000 lbs.
But what if you have a different range load cell, like maybe 2,500 lb.? You
can adjust the excitation voltage to 12.5V and get 25 mV out for 2,500 lbs.,
1 mV represents 100 lbs..

If you want better resolution you could get a meter that reads microvolts or
use a load cell amplifier.
http://www.ebay.com/itm/Load-Cell-Am...em519d34 1b6f

With the load cell amplifier you can adjust out the tare weight, such as
tare out the weighing platform. Then you can put your calibration weight on
your scale and adjust the gain for a reading that makes sense, you don't
want to adjust anything like 1 volt per pound if you intend to weigh 100lbs
unless your load cell amp can output 100 volts...

Or, you can do something like buy a cheap eBay 100 gram load cell and adjust
the amp for a voltmeter reading of 1.000 V with a 100 GRAIN calibration
weight. Of course you want to test closer to your load weight if you would
be using it for reloading.

You can use that info to hack a cheap Chinese scale, read the excitation
voltage and read the sense voltage with the calibration weight applied. If
the calibration weight isn't 100% of the scales capacity you'd have to
calculate the mV/V at full load. Then you can replace the load cell with
one in the range you want and calibrate with voltages close to the original
load cell calibration voltages.

RogerN