The divider to be now considered consists of a pair of legs connected with a spring, and is therefore named a springy divider: such an instrument is denoted by Fig. 283. Whenever it is needful to perform a great quantity of scribing arcs, or measuring, without any great care or precision being necessary, an ordinary compass is the proper instrument for the work, because compass-legs can be separated or closed together in less time than is required for the shifting of divider-legs; but to easily and precisely measure a length, or mark a length, and to properly scribe arcs and circumferences, springy dividers, having fine points, are indispensable. A spring divider is a very useful instrument for scribing and measuring, if properly hardened and pointed, to maintain the necessary sharpness while the tool is in use on hard surfaces. The mode of adjusting a divider to a length on a rule, or other measure, consists in rotating the thumb-nut until the two divider-points are nearly the required distance from each other ; and this is effected by putting the points near to the rule, but not touching it; after this, the final adjustment is performed by softly placing one point upon or into one of the marks on the rule, and while one point is held in the mark with one hand, the other leg is screwed in or out by gently working the nut until both points are felt to be in the marks, or seen to be on the marks, according to the particular rule in use while the adjustment is effected. To avoid wearing the divider-screw and nut to a needless extent when the legs require shifting a great distance, the two legs should be squeezed towards each other in one hand, while the other hand is used to rotate the thumb-nut during the time it is not in contact with the divider-leg.