Boss: pick the types
Pick the smallest types that still hold the data. Six hidden inserts decide whether your table is right.
task
Create meter(meter_id, serial, reading, read_at, unit, note): ids to 3 billion; serial up to 12 characters, required; reading up to 7 digits before and exactly 3 after the point, required; read_at a zone-aware instant, required; unit one of kwh, m3, l (a CHECK constraint), required; note optional.