6 BULLETIN 839, U. S. DEPAETMENT OF AGRICULTURE. 
PERSONAL EQUATION VARIATION. 
COUNTING THE SAME SLIDES ON DEETEKENT DAYS BY ONE ANALYST. 
Table 1 gives actual data obtained from counts made by each of 
two analysts working upon three slides which were prepared from the 
same bulk sample and upon which they made two counts on each of 
three successive days. 
Table 1. — Results of counts of same slides by two analysts on different days. 
Date. 
Slide. 
Analyst. 
Count 
No. 
Bran 
particles. 
Hairs. 
Total. 
1918. 
Jan. 7 
A 
A 
B 
B 
C 
C 
A 
A 
B 
B 
C 
C 
A 
A 
B 
B 
C 
C 
A 
A 
B • 
B 
C 
C 
A 
A 
B 
B 
C 
C 
A 
A 
B 
B 
C 
c 
Keenan 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
L 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
1 
2 
87 
92 
60 
60 
87 
81 
103 
114 
86 
80 
90 
87 
76 
82 
60 
49 
62 
64 
100 
96 
85 
77 
89 
83 
80 
83 
49 
53 
60 
77 
104 
106 
78 
77 
86 
86 
59 
64 
60 
58 
62 
74 
58 
52 
64 
58 
62 
57 
66 
69 
55 
48 
66 
68 
54 
56 
52 
55 
65 
59 
65 
66 
61 
57 
66 
71 
54 
55 
55 
55 
65 
62 
146 
Do.. 
do 
156 
Do.. 
do 
120 
Do.. 
do 
118 
Do.. 
do 
149 
Do.. 
do 
155 
Do.. 
Lyobs 
161 
Do.. 
.....do 
166 
Do.. 
do 
150 
Do.. 
do 
138 
Do.. 
Do.. 
do 
do _ 
152 
144 
Jan. 8 
142 
Do.. 
do 
151 
Do.. 
Do.. 
do 
do 
115 
97 
Do.. 
do 
128 
Do.. 
do 
132 
Do.. 
Lyons 
154 
Do.. 
Do.. 
do 
do 
152 
137 
Do.. 
do.. 
132 
Do.. 
do 
154 
Do.. 
do 
142 
Jan. 9 
145 
Do.. 
Do.. 
do 
do 
149 
110 
Do.. 
do 
110 
Do.. 
..;..do 
126 
Do.. 
do 
148 
Do.. 
Lyons 
158 
Do.. 
Do.. 
do 
do 
161 
133 
Do.. 
do 
132 
Do.. 
do 
151 
Do.. 
do 
148 
For the purpose of emphasizing certain salient points, the results 
recorded in Table 1 have been rearranged in Table 2, in considering 
which it is necessary to regard the different portions carefully. 
Keenan' s greatest variation in two counts of bran particles on a 
given slide on any one day was 17 points (slide C, Jan. 9, 1918), 
while Lyons' greatest variation was 11 points (slide A, Jan. 7, 1918). 
In the matter of counting hairs the greatest variation in the counts 
obtained on a given slide on any one day by Keenan was 12 points 
(slide C, Jan. 7, 1918), while Lyons' greatest similar variation was 6 
(in several instances). In these cases it appears therefore that the 
personal variation due to the error of counting probably would not 
exceed 17 points in the case of particles or 12 points in the case of 
hairs. 
