B. Means based on 
10 series of 10 
observations 
(i) Measuring 
mark diameter 3 
.42 minutes of arc. 
Target Visual 
Annulus 
Sp 
Angle (min.) 
width (min.) (Sec.) 
3.75 
0.17 
1.48 £ .1 
4.53 
0.56 
3.73 £ .2 
4.90 
0.74 
4.66 £ .6 
5.00 
0.79 
4.27 £ .3 
10.00 
3.29 
4.75 £ .3 
15.10 
5.84 
5.72 £ .4 
17.50 
7.04 
7.21 £ .5 
20.10 
8.34 
7.64 £ .6 
C. Threshold pointing errors for 
limiting annulus widths 
with different 
measuring mark 
diameters. 
Measuring Mark 
Annulus 
Sp 
diam. (min.) 
width (min.) (Sec.) 
2.23 
0.15 ‘ 
1.40 £ .1 
3.42 
0.17 
1.17 £ .1 
17.75 
0.18 
1.43 £ .1 
44.63 
0.15 
1.12 £ .1