"specifies where the numerical labels and tick marks for the second axis should be drawn.
For each axis, the LabelAt value gives the value on the other axis at which numerical labels and tick marks should be placed (remember that Plots suitable for use with AST_GRID may only have two axes). For example, in a celestial (RA,Dec) coordinate system, LabelAt(1) gives a Dec value which defines a line (of constant Dec) along which the numerical RA labels and their associated tick marks will be drawn. Similarly, LabelAt(2) gives the RA value at which the Dec labels and ticks will be drawn.
The default bahaviour is for the Plot to generate its own position for numerical labels and tick marks.
The LabelAt value should use the same units as are used internally for storing coordinate values on the appropriate axis. For example, with a celestial coordinate system, the LabelAt value should be in radians, not hours or degrees.
Normally, the LabelAt value also determines where the lines representing coordinate axes will be drawn, so that the tick marks will lie on these lines (but also see the DrawAxes attribute).
In some circumstances, numerical labels and tick marks are drawn around the edges of the plotting area (see the Labelling attribute). In this case, the value of the LabelAt attribute is ignored.