Without question, this can be the most complex and niftiest token possible in AllTopo.

In its simplest form, you can place %@% in a waypoint's description or note and AllTopo will display the distance and bearing to the previous waypoint In this example WP3 (at the south east corner of the section) has its description set to "%@%":

This tag accepts many optional arguments. If no arguments are included the offset and distance to the previous annotation are returned as shown above. The measurement spike defaults are used for distance units, north reference and projection unless overridden.

Sytnax:

 %@ "wpname" N NorthCode PROJ UNITS%

where:

"wpname":

is the name or description of the target waypoint. You may choose the annotation to compute bearing/distance to by:

1. Including the waypoint's Name or Description within quotes: %@ "WP1"%
2. Including an integer number to offset from the current annotation: %@ -2% uses the point before the last point.
3. Including both a waypoint Name or Description AND an offset: %@ "WP10" -2% uses the point two before the annotation named WP10.

N:

is the offset from the named waypoint. If no named waypoint exists N defaults to -1, if a named waypoint exists in the token then N defaults to 0.

NorthCode:

You may override/force the "North Reference" by adding "TN", "TRUEN", "MN", "MAGN", "SPN", "GN" or "GRIDN". :

TN
SPN_MT_NAD83
GN_13_NAD83

PROJ:

You may override/force the projection to compute distance by adding one of these projection codes: "UTM" "LL" or "SP". The projection code may contain optional zone and datum arguments like:

UTM_13_NAD83
SP_MT_NAD83
LL_NAD83

UNITS:

You may override or force distance units by adding any accepted unit code like "meters", "feet" or "chains".

By default both the distance and bearing are shown. If the "%@ ...%" token is changed to "%@B ...% then only the bearing is shown. If the "%@ ...% token is changed to %@D ...% then only the distance is returned. 

For example %@D% in the example above displays:

The tag: '%@ MN SP_UTN_NAD27 CHAINS "WP1"%' generates this display:

"From the south east corner to WP1 (the north west corner) is 111 chains 85.2 links at a magnetic bearing of North 57 degrees 22 minutes 59 minutes West, computed using Utah North Zone State Plane NAD27 projection."

The tag: '%@ 1%' displays the bearing/distance from the south east corner to the next waypoint (WP4 at the south west corner):