102 



LAND DRAINAGE 



137. Cautions. In taking a reading, the following 

 cautions should be observed : 



1. Always before recording a reading, observe the 

 bubble in the spirit level to be sure that the telescope is 

 level. 



2. If at any time the level should be disturbed, it should 

 be properly set and its height redetermined before taking 

 other fore-sight readings. In establishing the new height 

 of instrument, a reading may be taken to any point whose 

 elevation is known. 



138. Records and computations. Every reading 

 should be carefully recorded in its proper place in a table 

 provided for the purpose. If it is desired merely to find 

 the elevation of several points, the form of table given 

 below will serve the purpose. (See Table VIII.) Usually 

 the figures are introduced into the table as they are 

 obtained in the work of leveling, and the computations 

 are made later. 



TABLE VIII 



139. Directions and explanations. The following 

 points should be observed : 



1. That the elevation of point 1 had already been 

 established or assumed. It should be recorded after point 

 1, under elevation. 



