As each station is recorded, the readings should be mentally checked by 

 comparing the last place of the three measurements to determine if the differ- 

 ence between the upper stadia reading and the elevation is the same as the 

 difference between the elevation and the lower stadia. If a difference exists, 

 the readings should be rechecked. The importance of this check cannot be over- 

 emphasized, for it significantly reduces rod-reading errors and is a key to 

 accurate stadia surveying. When stadia are used in the surf zone, it may be 

 necessary to read all three measurements during one look through the instrument. 

 This can be done by first calling (out loud) the decimal places of the three 

 measurements, recording and checking them, and then taking a second look to de- 

 termine the whole number part of each measurement. This procedure can be accom- 

 plished easily after a little practice. 



When the data are reduced, the rest of the fieldbook should be completed 

 as shown in Figure 6. Each set of readings should be rechecked (using the 

 check described) and errors noted. One unique advantage of the system is the 

 built-in redundancy of the data. If only one of the three readings is in 

 error, it can usually be corrected by using the other two readings and the 

 pace count. A programable calculator or computer program to automatically 

 check and reduce the data is recommended. 



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Figure 6. Sample of reduced field notes. 

 V . ACCURACY 



The accuracy of any surveying method is highly dependent on many factors, 

 including weather conditions, Sun angle, fatigue, and the experience and care 

 of the IP and RP. The effect of errors also varies depending on the type and 

 magnitude of the error and on the analysis being performed. 



Assuming that the instrument is properly alined and level and that the level 

 rod is plumb, the elevation accuracy of a survey point using the stadia method 

 is equal to the accuracy to which the level rod is read. Distance accuracy is 

 dependent on the accuracy of the rod readings, with the distance computed as 



15 



