All spirit level vials and bubble vials contain a curved radius, even though it cannot always be seen. This allows the bubble to move to the highest point of the radius as gravity acts on the liquid inside the vial once it is level.
Plus I still use my Swedish adjustable level fully adjustable in both aspects. Made in Sweden at the industrial town of Eskilstuna, and possibly older than both of us. Eskilstuna was known as the Sheffield of SwedenÂ
