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731.—Caink's Rule for correcting inclines in chaining is the invention of Mr. Thos. Caink, C.E., of Malvern, Fig. 337. It is made four-fold, each fold being one link. The link is divided decimally along the inside of the rule. On the outer edge of the rule there is a scale marked degrees, a part of which is subdivided where the scale is open to read closer, that is, to 20 or 30 minutes. These degree divisions, which read up to 16° on one side of the rule, indicate the space from the end of the rule to be allowed in addition for the same degrees of inclination of the land up to 4 links of measurement. On the opposite side of the rule the inclination scale is carried from 16° to 22° 10′. For these higher numbers the length of the rule is first set off, and then plus such part of the rule as is indicated by the position marked upon it of the required number of degrees.
732.—To Use Caink's Rule.—The follower has a clinometer of one of the kinds shown, Figs. [260] or [264]. He notes at starting the position upon the face or body of the leader that corresponds with the height of his own eye. He takes the inclination of the land to this point of the leader's body while he is standing upright at one end of the chain and the leader standing at the other, noting the number of degrees shown by the clinometer. He then places the rule in the direction of the chain, with the number of degrees indicated, in front of the arrow, and moves the handle of the chain to this position. For the sake of verification, if he has a second arrow he may place it in the new position, which gives the true allowance. In either case the leader moves the chain forward by the amount required and places his arrow ready to continue the work. By this method it is seen that there is no after calculation or separate record necessary for undulating land, but the true horizontal position is given correctly at each chain measured. The same form of rule is made for feet and metres.
733.—In mountainous countries the eight links of the rule is insufficient allowance for common inclinations. Such countries are measured much more accurately by some system of subtense measurement, for which see [Chapter XII].; but where a small piece of sudden steep inclination occurs half a chain may be taken, and the number of degrees indicated upon the rule be doubled, so that the full rule, instead of taking 22° only, will take 44°.
734.—Steel Bands for measuring, termed steel band chains, are made in various forms in this country, and sold by nearly all opticians. They are much lighter than chains of equal strength, and are made of standard length. They are also lighter to use, being smooth and without any projection. On the other hand the reading is less distinct than with the chain, and they need more careful usage in chaining. They also require oiling before being put by. From the thinness of the metal they are altogether more delicate and less durable than the chains for hard wear; but it is thought by many to be a compensation that they are always of true length.
Figs. 338, 339, 340.—Steel bands and tapes.
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Fig. 341.—One link of steel band.