Fig. 102.—Details of Stanley staff; A bottom length, B middle, C top with dot figures.
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268.—The author designed another staff especially for his point index. This is shown above, Fig. 102. It has had a very fair popularity, being good both for distant and near sighting. In this staff for the close figures 11, 12, 13, on a 14-feet staff, which are with great difficulty distinguishable at a distance, the author employs dots only as before mentioned—one dot for the 11, two for the 12, and three for the 13, as shown C for the 12 and 13 in the right-hand figure. It must be remembered that a good clear staff is a great desideratum, as it means less size, weight, and cost in the level necessary to be used with it for equal exactness. A clear staff with a 14-inch level is quite equal to a complex misty one with a 16-inch level, with the advantage of saving expense in the purchase, and about 2 lbs. in the weight of the level to be carried in work.
269.—Our space will not permit the discussion of the various staff readings that have been designed, many of which are, in the author's opinion, superior to the Sopwith; but some variations are necessary occasionally for personal reasons. Some surveyors, from imperfect colour vision perhaps, strongly object to the red foot figure as being indistinct at a distance, hence in many patterns a clear black figure is employed. Some get confused with the number of equal lines of ·01 foot in the Sopwith, what is sometimes termed Sopwith's ladder. In this case these lines may be made unequal in different ways: several patterns have this peculiarity. Some persons cannot get over the inverted figure as seen in the telescope. In this case it would be much better, perhaps, to read with an erecting eye-piece to the level; but practically the manufacturer has to invert the figures. Other less important variations are common.
270.—Metrical Staves.—These are in this country generally made 14 feet, to keep the length the same as the tripod. The most approved patterns are shown Figs. 103 and 103A. In using the metre pattern at short distances often a complete metre cannot be taken in the field of view, so that there is a little difficulty in being certain to what metre interspace the subdivisions belong. To avoid this the author places a dot or dots after the decimetre figures that follow the metre—one dot for 1 metre, two dots for 2 metres, three dots for 3 metres. Thus 1·4 metre reads ·4; 2·4 metre reads :4. The dots need only be very small, as they are not required except for very close readings, that is, within about 30 metres: at 40 metres distance one complete metre comes into the ordinary telescopic field.
Fig. 103.—Metres and Half Centimetres.
Fig. 103A.—Centimetres.
Stanley's metre levelling staves.
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