Van Nostrand's engineering magazine . =25?1. Tak-ing the upper sign, £ 42, for a direct sub-scale, we may write /-=3, q* = S. Thecorresponding subscale is represented inFig. 7. The subscale division 7 coincides,and the final reading is inches. The number 24 affords several differentsets of factors, each of which could beused, giving a required compact subscale;but care should be taken not to make thesubscale spaces too small for distinct With a given least count, the best ofthe convenient forms is determined bythe cost of making the instrument. 1st. If the least count is large enoughto b
Van Nostrand's engineering magazine . =25?1. Tak-ing the upper sign, £ 42, for a direct sub-scale, we may write /-=3, q* = S. Thecorresponding subscale is represented inFig. 7. The subscale division 7 coincides,and the final reading is inches. The number 24 affords several differentsets of factors, each of which could beused, giving a required compact subscale;but care should be taken not to make thesubscale spaces too small for distinct With a given least count, the best ofthe convenient forms is determined bythe cost of making the instrument. 1st. If the least count is large enoughto be distinctly seen, it may be taken asthe subscale space of a simple taking the subscale as long as prac-tical convenience will allow, the numberof divisions on the main scale may be re-duced to a minimum, thereby giving aless cost of manufacture than with anyother convenient form of subscale. 2d. If the least count is to be as smallas possible, consistent with convenience,the scale space should be taken of a size Fig. vision. This compact subscale may bereduced to a vernier by simply dividingeach scale space into r equal parts. Theleast count is also divided by r. If the value of rq in (5) had beenprime we would have had either r = l org = l, reducing the compact subscale tothe vernier, § 27, or to the simple sub-scale, § 22. The compact subscale is thenimpossible; thus, if ^=30, and r=l, rq= 29 or 31 (compare §§ 40, 41). 53. Relative advantages of simple,vernier, and complex subscales. It isessential to ease of reading, with anyscale and subscale, that the coincidentsubscale division may be readily found;that the scale and subscale spaces shallbe large enough to be distinctly seen;that the divisions of both scales shall beplainly numbered; and that the entiresubscale shall not be too long to be crit-ically viewed at a single glance of the convenience of record, it is furtherdesirable that the scale space shall be aunit of expression, § 2, or some
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectenginee, bookyear1879
