[GIS] area values determined with field calculator become null when saving

Question

using field calculator in Qgis 1.8.0 to get the area, it shows just right at first but when I save it, the values become Null.

Answer 1

What Coordinate system is your shapefile layer in? If you have something in degrees, the area will be computed in square degrees (which does not make sense, and will be a very low value). Note that the project CRS can be different, but has no effect on $area.

If your layer CRS is in metres, try a greater value for width. 99999.99 m² may be too small for the areas. The formatting is only applied after saving, thats why you see the correct result at first.