Land Surveying and Levelling

to be only temporarily located. In case, however, of an accident in dropping an arrow, it becomes doubtful what is the exact number of chains that have been measured, and the position of a peg so placed limits the possibility of an error to a distance of ten chains, and then only this portion of the base line, in which a surveyor has the misfortune to lose an arrow, need be re-measured. Time is a more important element than the cost of labour and material in the use of pegs.

For the purpose of testing the chain employed in an extensive survey during the progress of any work, which will most likely stretch a little every day it is in use, it is well to fix two pegs upon a level piece of ground near a fence, and at a distance apart just sufficient to enable the outside of the handles of a correct chain when drawn tightly to touch the inner sides of the pegs. This arrangement is better than making the chain's length measure from centre to centre of the pegs, but the chain should be pulled quite taut, and the rings cleared of all dirt, and the links straightened, so that the chain may play freely along its whole length. If the chain has been previously pulled over a ploughed field upon a wet day the rings uniting the links will have become clogged with dirt and the chain will need washing, which can be effected by passing it through a stream carefully. The test distance may be set out very accurately with a level staff, or, better still, with two level staves placed end to end in measuring the line, provided each level staff has been previously tested upon the Government standards. It is sometimes well to keep a properly-tested spare chain in reserve, to be used only for the purpose of testing when a level staff is not near to hand, and the distance should be proved prior to each testing of a chain, as pegs have been known to be purposely moved by parties interested in opposition.

No survey can be accurate in which the base lines are ranged in the least degree curved, and in chaining up and down hill by a process called "stepping," as exemplified in fig. 4 (pages 14, 15), the steepness of the slope will regulate the distance between the successive points, P, R, S, as the chain can only be raised to a certain height by hand,