In many dialog box data entry fields, you may specify elevations, lines, distances or bearings by identifying existing point(s) that define the required elevation, line, distance or bearing, instead of keying in the actual values.
For an elevation, snap to and accept an existing point to specify that its elevation be used.
For lines, distances and bearings, snap to and accept two existing points, or key in two existing point identifiers separated by a double minus sign. The line, distance or bearing (as appropriate) defined by the two points will then be used.