spirit level
instrument with a sealed tube of liquid, designed to indicate whether a surface is horizontal (level) or vertical (plumb)
en-US/ˈspɪɹət ˈlɛvəl/
en-GB/ˈspɪɹɪt ˈlɛvl/
instrument with a sealed tube of liquid, designed to indicate whether a surface is horizontal (level) or vertical (plumb)