Marié-Davy’s 1854 sight for ships was two mirrors at 45° in a tube: look from the deck, see over the rail. Trench periscopes in 1914–18 were the same pair in wood. Submarines later added prisms and lenses; the first idea is still two flats.
Light comes in high and leaves low, or the other way around. Nothing is magnified unless you add glasses. This bench is the shift of the line of sight, nothing else.