. Siij . 
This type of instrument is available in 4 models with a choice of 
bubble reading and horizontal circle. 
The name “ Precision ” denotes that at the actual moment of reading 
the staff the telescope is precisely levelled by means of a micrometer or 
gradienter screw. It is therefore only necessary to set up the vertical axis 
approximately and this may be done either by ball joint or by the usual 
three-screw levelling arrangement. 
PRISM BUBBLE READER 
Maximum accuracy is obtained with a prism reading bubble. When 
the telescope is approximately level, half views of each end of the bubble 
are seen in the prism, Fig. B. As the telescope is levelled the views of the 
bubble approach coincidence and when the telescope is exactly level 
appear as Fig. A. 
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m 
B. 
This device eliminates all parallax and makes possible an accuracy 
of -01 of a foot in a long level traverse, with individual sights of up to 500 ft. 
The instrument is recommended for surveys of this order of accuracy 
for Town and Country Planning, railways, roads and irrigation, and in all 
such work where the use of a gradienter screw facilitates the setting out 
of gradients, etc., as shown by the following description :—