WHEELER — SECONDARY BASE IN GEODETIC SURVEYS. 



27 



ACCURACY OF THE LENGTH OF STANDARD TAPE FROM OLNEY BASE MEASUREMENTS, 



2<f<f = + 0.0455 



The probable error in the mean of the two measures of the base, 

 considering the measurements as in 36 independent sections, is 



y in. 



== 0.6745 ^ ^"" rr: ± 0.0719, and the p. e. of the east half of 



4 mm. in. ^ 



the Olney Base, not reduced to sea level, is = ± 3.215 = +0.127. 

 Combining these two probable errors we have «/(o.o7i9)2 +(0.127)2 



= + 0.146, and this divided by 36 gives the probable error in the 



in. 



value of the tape = + 0.004; o'" ^ ^" §97,237 parts of the tape-length. 



• See Professional Papers, Corps of Engineers, U.S.A., No. 24, pp. 287, 303, 304. 



