722.—Metre Chains are made 20 or 25 metres long. They are marked with tellers at every two metres with a plain ring at the metre. The tellers are generally of the inserted kind, Fig. 332. In taking measurements the sign of the teller is doubled: thus the ordinary 1 or 10 is counted 2 metres; the 2, 4, and so on. 20-metre chains in light steel, No. 12 B.W.G., weigh 4½ lbs.; strong, in No. 8 B.W.G., 9 lbs. 25-metre, light, 6 lbs.; strong, 11 lbs.
A land chain is generally secured for carrying by a leather strap with a buckle. Occasionally it is carried in a sailcloth bag with a strap over the shoulder.
723.—Standard Chains.—These are of the same form as the ordinary steel chain, but all the links are hard soldered after being adjusted link by link. They are not intended to be used for regular chaining, except it be for laying down rough base lines. Their special employment is to test chains, or to set out with two pegs on a straight piece of ground a standard length or station where the common chains in use may be tested daily. A standard chain is commonly enclosed in a box with a lock to prevent its accidental use for an ordinary chain.
724.—Arrows.—These are sometimes called pins. Ten form a set. They are shown with the chain in Fig. 330, and are commonly made of the same wire as the chain—No. 8 B.W.G. They are much better made one gauge stouter (equal to about 1/7 inch), and preferably of hardened steel than of iron. The common length is 15 inches. Where heath, stubble, or woodlands prevail 18-inch are better for use, and in some exceptional cases even 2-feet are very convenient. Surveyors going to new countries are recommended to take the longer arrows as well as those supplied with the chain. It is common either to tie a short length of scarlet webbing upon each ring of the arrow or to sew a piece of red flannel or bunting upon it to find it easily in long grass. Arrows are sometimes carried in a quiver with a strap over the shoulder, Fig. 334, which leaves the hands of the fore chainman free to remove obstructions where they occur.
725.—Drop Arrow, Fig. 335. Where ground is very hilly it is common to roughly level the chain by holding the lower position shoulder high, either by guess work or by using any kind of rough hand level or clinometer to ascertain this. The arrow is then dropped, and the point, held at first lightly in the ground, is pressed hard down or another arrow supplanted for it. The chain in this case is used in odd multiples of links as they occur, of which record is taken separately at each station. In going downhill a drop arrow answers very well. In going uphill a plummet to the last arrow is better. Some use the drop arrow as a plummet, carrying for this purpose in the pocket a piece of fine whipcord, with a bent hook tied to one end, to be used when required.
Fig. 334.—Quiver with arrows.
Fig. 335.—Drop arrow.
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