the amount of this error for accurate results. In is then placed in the viewer and the differ- 

 order to determine the amount of correction to ence, in feet, of the trace above or below the 

 apjily to depth for accurate work, tlie following zero depth line on the grid is the error for 

 procedures can be used in an emergency : which corrections must be made at all 

 With the sleeve all the way back, im- depth readings, 

 merse the thermal element in a cold and BT's that have a depth error of more than 10 

 then in a warm (less than 105° F.) bucket feet for a 200-foot instrument, 20 feet for a 450- 

 of water. This will cause a long zero depth foot instrument, or 40 feet for a 900-foot in- 

 line to be drawn across the slide. The slide strument should be replaced. 



C-9 



