WEIGHT VARIATION OF PACKAGE FOODS. qd 
mum variable error allowable by the specifications. The value se- 
lected for 7 is 50, since an average shipment usually contains at least 
50 packages, and experience has shown that 50 is a sufficiently repre- 
sentative sample. 
_ Then the calculated maximum error on the average weight of a 
representative sample of 3-pound packages is— 
= 02250 
+ (0.062)? + (0.062)? + (0.034)? + (0.062)?+ 508 or 0.148 ounce. 
75-POUND PACKAGES. 
The specifications of good commercial practice require that a 75- 
pound package shall be weighed gross and tare on a platform scale 
of not more than 750 pounds capacity, carrying a 50-pound beam 
eraduated to one-fourth pound, and that the poise of this scale be set 
to within one-fourth of a minimum graduation, and that no error 
ereater than one-half the sensibility reciprocal be made in estimating 
the exact balance. 
Then the maximum constituent errors as read from the tolerance 
tables and specifications are: 
Constant errors introduced into every package: 


On tares (assumed to be 15 pounds)— Ounces. 
Crm OTAGO ee A eps ic Mies Raed cs ares a clare Be es age eo 0.00 
be Onebeam:, (Col. 3. Lable:3) tor 50> poundsior less... -22...-2-6-+..2--5 == 1.00 
e= Counterpoise weiehts times ratio of scale... -.... 2... 52... ee-:--- 2+: . 00 
On gross (net plus tare: 75 + 15, or 90 pounds)— 
@-uOinerationCol-24 hable:3) tor 50) pounds sa.2-. --.-6-sicis'e cee ee ss 22a 2 oe . 50 
er Onepeamn Colas. lables stor50 pounds or-less 722... 5.) 2. ecae52 5 +s 1.00 
jf. Counterpoise weights times ratio of scale (Col. 3, Table 4) for 50-pound 
counterpoise, which is an 8-ounce weight on a ratio of 100:1, or 3 grains 
FUMES LOR: ok soe SE RN Mapa le oe Ret Pepe oe a ee ee aes . 69 
Variable errors due to the manipulation of the scale: 
On tares— 
g. Since the weight of the tare can not be changed, it will be weighed to the 
nearest graduation of the scale, and the reading may bein error by one- 

half the minimum graduation (4 of 4 ounces).......--.-..------------ 2.00 
h. One-half of the sensibility reciprocal (one-halfof twice the minimum gradu- 
ariongebablers).)i(> Ol SO OUNCES) 222. 055. cu ede oss occa ce sees eae ae 4.00 
On gross— 
z. One-fourth of a minimum graduation for setting of poise.........-......- 1.00 
k. One-half of the sensibility reciprocal (Table 3) (4 of 8 ounces)..........- 4.00 
The constituent constant errors and the constituent variable*errors 
will each combine according to the law of propagation of errors as in 
the case of 3-pound packages, and the calculated maximum error on 
— wy single package will be given by the direct sum of the two results, 
that is— 
V (a)? + (6)? + (©)? + @? + ©? 4+ FP + VQ? + (h)? + @? + EP 

or 
(0.00)? + (1.00)? + (0.00)? + (.50)? + (1.00)? + (.69)2 + 
+/ (2.00)? + (4.00)? + (1.00)? + (4.00)2, 
which is 7.73 ounces. 
