Crack meters are relatively low-tech devices that can be installed across a structural crack to measure movement between the sides of the crack. The meter consists of two pieces that each attach on a separate side of the crack, but overlap in the middle, more or less right over the crack. One side has a grid of 1 mm squares, and the other piece is clear except a red cross that lines up over the middle of the grid. The meter can be checked over time to see if the red cross has moved relative to the underlying grid.