The official data description of the recently updated GIMMS NDVI3g record describes the grid parameters of the dataset as follows.
grid-name: Geographic Lat/Lon pixel-size: 1/12=0.0833 degrees size-x: 4320 size-y: 2160 upper-left-lat: 90.0-1/24 upper-left-lon: -180.0+1/24 lower-right-lat: -90.0+1/24 lower-right-lon: 180.0-1/24
This means (at least to my understanding) that in x-direction, the cell size equals
> (180-1/24) * 2 / 4320  0.08331404
whereas in y-direction, the cell size equals
> (90-1/24) * 2 / 2160  0.08329475
I.e., the single grid cells are not entirely square-shaped. Am I missing something in my calculation or does the officially described pixel size of "1/12=0.0833 degrees" simply result from rounding effects of the manually calculated edge lengths in x- and y-direction?