Numeric offsets only.
Each field is a signed UTC offset in hours (typical range clamped to −14…+14 for sanity). The page shows B − A as the hour difference you would add when moving from offset A to offset B (educational; not a full DST rules engine).
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.