The Beveled Horizontal Limb 



All of the larger Theodolites and Alt-azimuths, including the 

 7-, 8-, 10- and 12-inch models, have been habitually made 

 with beveled plates and supplied with the European 3-screw base. 

 Some manufacturers have argued laboriously against the adoption 

 of the beveled limb for every conceivable reason except the para- 

 mount issue which involves increased cost of manufacture. 



It may be consistently contended that in looking straight down 

 on the line of separation between vernier and limb, when the read- 

 ing edge is worn, one may not make quite so careful an estimate of 

 a coincidence as when looking toward the scales at an angle of say 

 M) . On the other hand, the slanting line of vision against a flat 

 limb is what offers the opportunity for parallax in reading when 

 the fit becomes imperfect by abrasion. 



Fig. 75 



There can be no doubt that the beveled limb is more readily- 

 accessible and that the eye can be brought near to it without inter- 

 fering with other paits of the instrument. This is especially true 

 of the more finely divided circles that are supplied with powerful 

 attached magnifiers. There is no reason known to us why the 

 bevel limb cannot be just as accurately and durably made but it 

 costs more to build than the flat limb. Diagrams are always of 

 technical interest if they are not purposely calculated to mislead the 

 reader. The diagram shown in Fig. 75 represents the latest method 

 of applying this principle to the 6-inch Theodolite, as illustrated in 

 Fig. 77. 



The beveled homontal limb offers the best arrangement for 

 the adoption of the Attached Magnifiers or fixed reading glasses, 

 as they are sometimes called. These are an adaptation of the 



