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The lat/long equivalent of T639 is 0.28125 deg (360/(2*(639+1))). However, the GRIB1 format only supports three decimals, so we recommend that you round the resolution to 0.25 deg (giving 360/0.25=1440 equally-spaced grid points). Specifying a higher resolution is technically possible, e.g. as 'grid':'0.1/0.1', but this only oversamples the data and does not improve the accuracy of the data. Specifying a coarser resolution is also possible, but in this case, care should be taken to avoid aliasing.
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