A spirit level is a must if you want your home to have straight, even lines, but what is that bright-green liquid inside the bubbles? It's not just water.

To check if the floor is level, Hambidge suggests, “Use a carpenter's level (typically longer than a spirit level), marking out any uneven areas with chalk.

When a bubble, or spirit, level is level, what does that mean relative to Earth? Pat French Longdon-upon-Tern, Shropshire, UK There is a well-known story of a gentleman who held that Earth was flat.