Constant MAX_POINTS 

pub const MAX_POINTS: u64 = _; // 16_777_216u64

The most grid points a field may have: 2²⁴, about 16.8 million. The largest common grids are well inside it (GFS at 0.25°, about 1.04 million; ECMWF at 0.1°, about 6.5 million). A field of 0 bits has no packed data to bound its grid, so this bounds what Field::values allocates: 16 bytes a point, up to 256 MiB for one field, whatever the file’s size. Field::value reads one point of a simple-packed field and allocates nothing.