STANDARD COMPASS. 13 



will show the number of degrees of dip or rise. This 

 is not the same as ' ' per cent of grade." The difference 

 is shown on page 40. Another method is to lay the 

 edge M on the level plane-table board and, revolving 

 the rim vertically, take a sight through the slots K. 

 The angle of dip or rise may then be very closely ap- 

 proximated by reading the graduation on the rim. In 

 some of these instruments the cover of the socket, at 

 the ball joint, is cut away on one side, permitting the 

 spindle to be tipped over and the compass revolved in 

 a vertical plane. The sights may then be used in con- 

 nection with the clinometer. This altered socket will 

 be issued when specially requisitioned. 



Right angles may be turned accurately without the 

 use of the compass by two methods: (1) By drawing a 

 line on the plane-table sheet on the edges P and then 

 turning the instrument 90 until the edge M coincides 

 with the line, or (2) the slots ^may be used without 

 moving the instrument, as they are placed exactly 90 

 apart. 



This instrument should give good results if used and 

 treated with the care which is necessary for any well- 

 made and carefully adjusted instrument. The cus- 

 todian should keep it clean, but should not oil it, though 

 it may be wiped occasionally with a slightly greasy 

 piece of muslin. The needle should always be clamped 

 when not in use, and the hair sight should always be 

 closed down first so that it will be protected by the 

 slot sight. The cover glass may be removed by tak- 

 ing off the sights and then the surrounding rim, which 

 is provided with small brass screws which travel in a 

 channel cut into the outside of the compass box. It is 



