Level 2 Help for GRIDCK

The grid is detected automatically and has a tolerance for
points being out of regularity on the grid.  Each point is
predicted by its two previous neighbors and the distance
from the predicted to the actual is ratioed to the neighbor
grid distance.  GRIDTOL is the maximum ratio allowed.

You can be generous with this parameter, say 10 or 20, but
keep it smaller than the nah or nav by half.  The row or 
column that is found must match the length of the other rows
or columns and (nah+1)*(nav+1) must equal the total number of
points.