The steelyard is a Chinese invention.
As early as 200 B. C., China began to make a scale of
this type big enough to weigh several hundred pounds.
The steelyard consisted of the following parts: an arm,
a hook, lifting cords and a weight. 
The arm or beam measured about 1.5 metres long, graduated
with the weight units-jin and liang*. The hook, hanging
from one end of the arm, was used to lift up the object
to be weighed. Hanging from the other part of the arm
was the freemoving weight, attached on a looped string.
On the arm was fixed one, two or three lifting cords,
placed much closer to the hook than to the other end.
Anything to be weighed should be picked up by the hook,
while the weigher lifted up the whole steelyard, holding
one of the cords. He then slided the weight left or
right until he found a perfect balance of the beam.
He then read the weight from the graduation mark on
which the weight-string rested.
This kind of steelyard is still in widespread use at
market gatherings in China. They may be made in varying
sizes working by the same principle, with the large
ones to weigh foodgrain in bulk, pigs or sheep or their
carcasses, and medium-sized  ones
for smaller transactions. There is also a miniature
steelyard only about one third of a metre (about 1 foot)
long, graduated with liang and qian**. Used to weigh
medicinal herbs and sliver or gold , it first appeared
about 1,000 years ago.
The steelyard is more convenient than the platform
scale. Not only can it be carried around easily, but
there is also no need for a whole set of weights. Corresponding
to the lifting cords are different sets of graduation
marks on the arm for different measuring ranges.
It is perhaps worthwhile to mention that the equal-armed
platform scale appeared in China earlier than the steelyard
with a sliding weight. A scale of the former description
with a complete set of weights was discovered lately
from a tomb near Changsha , Hunan Province, which dates
back to the Period of the Warring States (475-221 B.C.).
It is in size similar to those in use today and its
component parts are found to be in good proportions.
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