#Directions# are indicated on charts both by the projection lines and by compass roses. Nearly all charts are now oriented with the meridian, that is, north is the top of the chart, and on a mercator chart the east and west border lines are parallel with the meridians and the north and south border lines with the parallels. Formerly many charts were not so oriented. Some of these are still in use and can readily be recognized by the diagonal or inclined direction of the projection lines with respect to the border of the chart. Of course directions must not be referred to the border lines of these diagonal charts, and scales along such border lines must not be used. Directions with respect to true north may always be referred to the projection lines of the chart, but on a polyconic or polar chart a direction must not be carried so far from any projection line as to introduce error on account of convergence of the meridians. Compass roses are placed on charts to facilitate the taking off or laying down of directions, though in some respects their use is less accurate and convenient than the use of protractors, referring to the projection lines. The British charts and many of those of the United States Coast Survey have only magnetic compasses, with degrees outside and points inside, the former graduated to 90°. These are engraved on the chart with the magnetic variation for the date of publication, or for a few years in advance, and give the annual change in the variation. Because of expense of engraving they can be changed on the charts only at intervals of some years, and until this is done allowance for the change in variation is to be made if important. The German charts and those of the United States Hydrographic Office now have a threefold compass, the outer one degrees true, the middle degrees magnetic and the inner points magnetic; the degrees in both cases are graduated to 360°, reading from north through east, south, and west; thus northwest would be stated as 315° instead of N. 45° W. Small scale charts covering extensive areas have no magnetic compasses. They sometimes have true compasses, and usually have the isogonic lines, or lines of equal magnetic variation, marked on them, from which the variation at any intermediate point can be estimated. #Depths.# The unit used for depths is always stated plainly on the chart, and it is important to note this carefully, as the British, American, and Japanese charts use fathoms for some charts and feet for others, and most other countries use meters. Some of the earlier charts of the United States coast have the depths inside of the 18-foot curve in feet and outside of that curve in fathoms.