The Orient 1 value entered in the traverse dialog for a borehole traverse, is required because the beta angle measured for each discontinuity on the core, must be measured with respect to some reference line along the length of the core.
If the reference line is the TOP of the core (i.e. a line along the physical top of the core), then Orient 1 = 0. If the reference line is along the BOTTOM of the core, then Orient 1 = 180 degrees. These are the most common situations. However, Dips allows the reference line to be located at any position with respect to the top of the core, hence an “arbitrary” value can be entered, if the reference line is at some arbitrary position (e.g. 45 degrees from the top line of the core).
The Orient 1 value serves to orient the rotational position of the core, with respect to the borehole. Without the reference line, you do not know how the core was positioned with respect to the borehole, therefore this is always a required input for oriented core analysis.
Note: for a vertical borehole, there is no longer a “top” or “bottom” of core, therefore you should enter Orient 1 = 0, and the Orient 3 value is used to determine the position of the reference line. As stated in the help for Orient 3: For a vertical borehole, use the clockwise angle from true north to the reference line, looking along the direction of borehole advance.