BAR-SUBTENSE SURVEY. 
115 
Signals observed. 
Reading of A 
vernier. 
Differ¬ 
ences. 
Subtended 
angles. 
Error of 20 ft. bar 
—o*2 of an inch. 
0 < If 
0 / • 
1 n 
Back station 
A 
1.26 14 20 
Right-hand disc 
B 
206 26 30 
» » • 
b 2 
209 48 30 
3 22 O 
d 
20 12 
» >5 • 
b 3 
213 IO 15 
3 21 45 
d% 
20 10*5 
» >» • 
b 4 
2l6 32 5 
3 21 50 
d 3 
20 II 
Back station 
a 2 
136 19 55 
M 20 11*2 
= X. 
(30 repetitions) . 
10 5 35 
From Table, 
Chains . 
. 51 60* 
10 5 35 
Correction f 
• 
. - 4 
Subtended angle 
* 
20 11*2 
Corrected distance . 
5156 
O / " 
Traverse angle :—B —A (= B 4 —A 2 ) 80 12 to 
x 
Angle at station 1, between back station) g 0 2 5 
and centre of bar at No. 2 .. ../ 
A 10-foot bar with an error of O’2 of an inch would give— 
Chains .. .. 25*80 
Correction .. — *08 
Corrected distance, ch. 25 *72 
A 2-foot bar with an error of 0 * 02 of an inch would give— 
Chains .. .. 5*16 
Correction .. — 1 
Corrected distance, ch. 5*15 
* For actual use the distances have been tabulated between 2 and 180 chains, 
f Bar -- 20 ft. = 30 '3 Iks. log. 1*48144 
20' 11 *9" cosec. 2 ■ 23122 
i 2 
51*60 log. 3 '71266 
