chart. The object must be sufficiently far off—say, at three miles—so that the bearing will not appreciably alter as the vessel swings. Then by slowly carrying the cable or mooring-rope down one side of the vessel to her stern and back to the bow along the other side, the tide can be made to swing her right round; or if there is no tide her head can be gently pulled round with the dinghy; or again, if one is not pressed for time, one can make one's observations for deviation as the vessel swings naturally to ebb and flow. As her head is brought in succession on to each of the thirty-two points of the compass, careful bearings of the object must be taken—the compass, of course, being stationed in the exact position in which it will be used at sea. If all the bearings agree with each other and with the correct bearings, there is no deviation; but if they differ, a table must be drawn up showing the exact deviation for each point of the compass towards which the vessel's bow was directed; and when shaping one's course at sea this table must be referred to, and proper allowance must be made for the error. The rule is—with westerly deviation allow to the left, and with easterly deviation to the right. For example, if one desires to sail N.E., and the table shows that with the vessel's head pointing N.E. her compass has an easterly deviation of one point, one will have to steer one point to the left of N.E.—that is, N.E. by N.
The following example will show how a Deviation
