To obtain a grid point, fill out only one latitude and one longitude and select [halfway grid points]. This gives the grid point nearest to the point given.
Selecting [interpolated] with only one latitude and one longitude gives a simple bilinear interpolation. You can restrict the interpolation to land points or sea points only if the land/sea mask is available.
By filling out two coordinates you request the area average between these coordinates. Only whole grid points are supported at the moment, the option [half-way between grid points].
The coordinates should be entered in ascending order, so -60°E to -30°E defines an area of 30° longitude, but -30°E to -60°E defines an arrea of 330° longitude. As a convenience, the latitudes are swapped if they are entered in the wrong order.
The actual coordinates used are always mentioned in the caption of the next page. These are normalised to be in ascending order and give the boundaries of the grid boxes used in the computation.