88 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
cated weights are always in proportion. If, for instance, one sample 
weighs twice as much as another, the scale must show that fact. 
Specifically, this means that all of the weights and the poise must 
be in proper proportion. Such a condition can be readily determined 
on platform scales by any scheme which allows the same piece or the 
same quantity of material to be weighed in turn with the different 
loose weights and with the poise. 
CHECKING THE PLATFORM SCALE 
Consider, for example, a 100-pound silk scale that has a single 
poise and a beam graduated to 2 pounds by hundredths of a pound, 
and loose counterpoise weights of 50, 20, 10, 10, 5, 3, and 2 pounds, 
respectively. This scale can be checked up as follows: Balance the 
beam accurately, set the poise at 2 pounds, and place just enough 
material on the platform to balance. Then return the poise to zero 
and put the 2-pound loose weight on the counterpoise. The beam 
should balance again. If it does not, the 2-pound loose weight and 
the poise are not of the proper relative weight. To ascertain the 
degree of error, balance the beam by changing the weight of the 
material on the platform. Then remove the 2-pound loose weight 
and balance the beam again by sliding the poise. The reading on 
ihe scale then indicates the weight of the 2-pound weight in com- 
parison with that of the poise; if the loose weight is heavy enough 
to make it necessary, set the poise at the 2-pound reading, remove 
material from the platform until the beam balances, and get the 
weight of the material removed. Having checked the 2-pound 
weight against the poise, check the 3-pound weight by putting 
enough additional material on the platform to balance at 3 pounds 
with the poise set at 1 pound and the 2-pound weight on the counter- 
oise. Remove the 2-pound weight, return the poise to zero, and 
place the 3-pound weight on the counterpoise. This scheme of com- 
parisons may be continued through the entire capacity range of the 
scale. It is most convenient, in securing the final balance of the 
beam at the different weights, to use a pan of shot, sand, or water for 
the material. 
CORRECTING ERRORS IN THE WEIGHTS 
After all the loose weights have been compared with the poise, 
consideration may be given to the correction of errors. If all the 
loose weights seem to be either too hght or too heavy, the poise 
itself probably is too heavy or too hight, and hence its weight should 
be corrected. ‘The usual method of lightening is by drilling or fil- 
ing; weight may be increased by adding metal, usually lead or solder. 
Care should be taken to see that any metal added will stay in place. 
If the errors in the loose weights are erratic, the assumption is 
that the individual weights are incorrect, and they should be 
changed accordingly. 
CHECKING THE BALANCE 
A balance in which loose weights are used can be checked, after 
the beam has been balanced with the pans empty. simply by inter- 
changing the contents of the two pans. If the pans were in balance 
