TEST WEIGHT OF GEAIN : ACCUEACY OF TESTING APPARATUS. 



11 



METHOD OF DETERMINING ACCURACY AND SENSITIVENESS OF 



BEAM. 



Before attempting to check the accuracy of the beam the base 

 of the tester should be leveled and, if it is of the standard type with 

 horizontal arm and trig loop, this level should be tested by examin- 

 ing the position of the projection or pointer on the end of the beam 

 in its relation to the trig loop. The pointer should be in the center 

 of the trig loop both horizontally and vertically when the empty 

 kettle is on the beam and the counterpoises are at zero. If this is 

 not the case the leveling screws should be adjusted until it is true. 



There are two methods of checking the accuracy of the beam 

 graduations. In the more simple and direct method a special set 

 of 14 accurate testing weights is used while in the other method an 

 ordinary set of metric weights is used. 



Fig. 8. — Special weights used in determining the accuracy of the beam in the weight- 

 per-bushel testing apparatus. In making the test these weights are placed in the test 

 kettle. 



The 14 special weights illustrated in figure 8 are marked to repre- 

 sent the following number of pounds per bushel : 60, 50, 40, 30, 20, 

 10, 5, 2, 2, 1, 0.5, 0.2, and 0.1. Each weight actually weighs ^ of 

 its marked value. To test the beam place any weight or combina- 

 tion of weights, within the range of the beam graduations, in the 

 kettle and bring the beam to balance by means of the counterpoise. 

 The combined readings of the counterpoises should now equal the 

 combined represented weights in the kettle, and the difference be- 

 tween the weight represented in the kettle and on the beams, if any, 

 i- the error of the beam. 



It is equally essential in making correct weight-per-bushe] tests, 

 especially on •• line " samples, thai (lie beam should not only indicate 



an apparently correct reading when a given weight is placed ill the 

 test kettle hut that it should also he sensitive to within one-tenth 



of a pound per bushel. That is, the beam should he sufficiently sen- 

 sitive to move either up or down noticeably, and in the case of a 



