This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
In laying out a garden, or in reducing a piece of undulating ground to the level of a bowling green, cricket pitch, or tennis ground, the art of levelling is a useful accomplishment. A simple method of taking levels, and one usually sufficient for most horticultural and agricultural purposes, is by means of " borning " or "boning:' rods and spirit levels. Three boning rods are used, each consisting of a straight piece of smooth batten about 4 ft. long, with a shorter crosspiece on top, the whole resembling the letter T. Sometimes the boning rods are all alike, but there are variations. The crosspiece in some cases is an inch wider than in others, and a small sighting hole is pierced in it just 1 in. from the upper edge. On looking through this hole, and sighting over the second and third rod (each of which is held by an assistant) it is possible to see whether the third rod is higher or lower than the second one. This latter must be arranged on the same level as the sighting one by means of a spirit level, after which the third rod may be shifted about to various spots. Pegs are driven in at the various points until the tops are at the required level. One can then see at a glance, by the length of the pegs sticking out of the ground, which are the higher and lower places. The diagram (fig. 402), shows another set of boning rods. The sighting hole is in a plain upright rod without a cross piece, while the end rod has a rounded cross piece, with the portion above the proper level painted white. This makes it much easier for the eye to distinguish the edge of the second or intermediate rod when sighting through from the first on to the third.
Fig. 402. - Boning Rods.