D = Ki X (US-LS) + K2 (1) 



where 



D = distance 



US and LS = upper and lower stadia readings, respectively 



Ki = stadia multiplier (usually K^ = 100) 



K2 = focal length constant which varies with the instrument 



Equation (1) shows that to obtain distance to the nearest 0.1 foot, each stadia 

 reading must be made to the one-thousandth place. Generally, accuracies to the 

 nearest 1.0 foot are acceptable, but rod readings to the nearest 0.01 foot are 

 required. 



Since stadia surveys require three times the number of rod readings as in 

 a level and tape survey, rod-reading errors should be anticipated. Rod-reading 

 errors can be virtually eliminated by performing the mental check previously 

 described. If the rod is plumb, and careful readings are made, then 



US-E = E-LS (2) 



where E is the elevation reading, and 



US-2E + LS = e = (3) 



If e ?^ 0, then the value of e provides some measure of the quality of 

 the stadia readings for a single survey point. Although an e equal to zero 

 is desired, on long shots an e equal to 0.015 unit is generally acceptable. 

 The effect of conducting the mental check is dramatic — of 500 points surveyed 

 with or without the check, the number of points with unacceptable values of 

 e dropped from 14.4 to 2.9 percent. Interestingly, most of the 2.9 percent 

 were for points with an e > 0.10. Errors of this magnitude indicate distance 

 errors equal to or greater than 10 feet; however, they are easily corrected by 

 estimating the true distance using the pace count. 



During repetitive surveys of the same profile, the stadia method showed 

 acceptable repeatability and an ability to measure profile volume to an accu- 

 racy of +0.5 cubic yard per foot (±1.25 cubic meters per meter), though this 

 value is dependent on profile length. 



VI . SUMMARY 



A method for efficient two-person stadia surveying has been described. 

 Using these procedures, a survey of a single beach profile line can be completed 

 in approximately 15 to 20 minutes, including instrument setup. A high degree of 

 accuracy can be maintained if : 



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