Levelling Staves or poles, are those employed in levelling, serving to carry the marks to be observed, and at the same time to measure the height of those marks from the ground. They usually consist of two mahogany staves, 10 feet long, in two parts, that slide upon one another to about 5 1/10 feet, for the greater convenience of carriage. They are divided into 1000 equal parts, and numbered at every tenth division by 10, 20, 30, etc. up to 1000; and on one side the feet and inches are also sometimes marked. A vane slides up and down upon each set of these staves, which, by the pressure of springs, will remain stationary at any part. The vanes are about 10 inches long, and 4 inches broad; the breadth is first divided into three equal parts, the two extremes are painted white, the middle space divided again into three equal parts, which are ess; the middle one of them is also painted white, and the two other parts black; and thus they are suited to all common distances. These vanes have each a brass wire across a small square hole in the centre which serve to point out the height correctly, by coinciding with the horizontal wire of the telescope of the level.